UPDATED: See a few additional comments from RunKeeper's Jason Jacobs at the end of the review

So I started running a month or so ago. Mainly because I stopped working near my gym and needed to find another gym and wasn't sure which gym to join and all the while kept eating and drinking and eating some more and, well, looking for a gym and blogging about mobile tech doesn't really keep one fit, now does it? So one day I just put on my shoes and ran to an arbitrary spot and back and six or seven weeks later I'm somehow still at it.

Much of why I'm still at it is, I think, thanks to smartphone GPS fitness apps like RunKeeper. As I blogged about a few weeks ago, these sorts of apps are a godsend to folks who like to walk, run, or bike while listening to music and also tracking the time and distance of their activities - and, of course, while keeping their phone with them just in case it's needed.

While Apple and Nike's "Nike + iPod" system is probably the best known fitness tracker solution, several companies have tapped into the built-in GPS systems of modern smartphones to create fitness tracker apps that don't require additional hardware. FitnessKeeper Inc.'s RunKeeper is one such app for Apple's iPhone. I've been using both RunKeeper Free (Free) and RunKeeper Pro ($9.99) to track my runs for the past month, and while it has its flaws it's a nice option for iPhone owners who don't want to mess around with the additional hardware necessary to run Nike's system.

RunKeeper also offers a few nifty tricks that Nike + can't match, including the ability to track "non-stepping" activities like cycling and boating, and location data tracking, which powers RK's Google Maps integration. The latter is perhaps my favorite thing about the app, as it lets me track my route back on the computer, including speed and elevation plotted out over time. In other words, I can see just how slowly I climbed one hill or another on my run.

RunKeeper is pretty easy to use. Download and install it, fire it up, create a free account, wait for GPS to acquire a signal, and then tap the big "Start" button. Then you walk, run, bike, or otherwise move around, and when you're done you press "End." RK tracks your elapsed time and distance, shows you stats during and at the end of your activity, and also uploads your workout data to its servers. When you're not busy sweatin' it out, you can view your workout history - with maps - on your iPhone and on any flash-compatible Web browser.

There's more to it than that, of course. You can share your activities with the RK community via Facebook and twitter. You can use the Pro version to post geotagged photos and status updates along your routes (say, if you're on a bike tour) and share those photo-enhanced maps with your peeps. You can also use the pro version to speak audio stats to you as you workout and even program audio-guided interval workouts for specific training needs.

So great, lots of features. But does it work? Yeah, it does. Pretty well most of the time, in fact.

I started out with RK Free, which is basically RK Pro minus the audio voiceovers, custom workouts, photos/status updates, and playlist integration. And plus advertising. RK Free is a pretty good option for most folks, I'd think, unless you really want the Pro versions's softly encouraging female voice speaking splits to you every five minutes. Of course, now that I've got the Pro version I've come to really like those voiceovers, but that's how it goes, right? While RK Pro offers iPod playlist integration, which lets you launch a playlist when you hit RK's "Start Activity" button, you can also just use your RK Free with your iPod the old-fashioned way: by running the iPod in the background while RK Free runs on top of it.

So long as you've got decent GPS and network coverage where you're working out, both versions of Run Keeper do a nice job of tracking what they're supposed to track. My first couple of weeks running with RK resulted in alarmingly quick battery drains, and an email to the RK folks suggested that I might be in an area with weak 3G coverage and that I should disable 3G while using the app. I did, and it helped with battery life. More recently, AT&T upgraded cell tower coverage in my neck of the woods, and so I turned 3G back on while running. Wouldn't you know it, no more battery drain problems!

My runs have ranged from one to four and a half miles thus far. So far as I can tell, RK has tracked them accurately, though I did have one partially-mistracked run and another false start that - for whatever reasons - didn't get tracked at all. For a couple of days in a row, RK Pro would crash whenever I tried to enter its Preferences menu to integrate an iPod playlist, but my iPhone 3GS was having other issues around that time, as well. A clean system restore fixed all of the phone's problems, including the RK Pro issue.

My install of RK Pro is set to provide audio data every five minutes: Elapsed time, elapsed distance, and current pace. Current pace is useless - the RK folks tell me they're working on an improved algorithm for calculating pace, but for now it's pretty dicey at best. Sometimes my current pace is a sub-five minute mile, and others it's 13 minutes or more. My real pace is always somewhere in between, and I'll leave it at that. But the other data is nice - hearing my elapsed distance is a nice motivator, and just knowing that I've been out there for, say, 25 minutes lets me know when it's time to start heading for home - or if I should push myself to do another five or ten minutes on the road.

And like I said, the best part is checking the runkeeper.com website after a workout. The site shows weekly and monthly activity overviews as well as detailed data and maps for each workout. A much-needed feature currently in Beta is the ability to edit activity maps to correct erroneous GPS data. Right now you can change data points along a route to correct or extend a path, but you can't add data points or otherwise alter the elapsed time of an activity. So I can change a one-mile run to a four-mile run if the GPS tracking failed, but I can't also change the elapsed time of that run to reflect the corrected distance.

The guys behind Run Keeper are working hard on bug fixes and updates, and do a nice job of keeping their blog updated. So far they've had success in the Apple App Store Health and Fitness rankings, and it's deserved: RunKeeper is a nice app that combines useful fitness tracking and clever GPS data features with a homegrown feel (and I mean that in the best of ways). I can't vouch for RK's accuracy on the elite athlete level, but for the casual runner or enthusiast who owns an iPhone and wants a way to log his or her activity miles, both RunKeeper Free and RunKeeper Pro offer compelling solutions. Definitely recommended.

App Store Links: RunKeeper Free and RunKeeper Pro.

Update: Jason Jacobs, the man behind RunKeeper, dropped me a line just after this review was posted. A few comments of interest from him:

First, with current pace, we agree it can be choppy, especially at lower speeds.  This should not affect the averages/totals at the end of your activity.  We will soon be adding average pace during your activity, so you can see (and hear in RK Pro) what kind of pace you are keeping as you go.  Second, the crashing you experienced had to do with a bug in RK Pro around iPod playlist integration.  A delete/reinstall would resolve (as you noticed) and this has been fixed completely in the current build of RK Pro (1.6.0.12).