First off, I think Engadget Editor-in-Chief Joshua Topolsky did a great job in this spot.  I was super-jealous before watching the video - both b/c Josh got to be on Fallon and because he got to play with a Pre - but by the end I really just enjoyed his wit and Fallon's own ease with his inner-dork.  That said, the spot does play somewhere between "paid placement" and "infomercial."  But Josh assured me, via Twitter just now, that Palm wasn't behind the whole thing:

Phonedog_Noah: @joshuatopolsky okay, seriously, did palm sponsor this?

joshuatopolsky: @Phonedog_Noah: No! Jimmy asked for the Pre by name and we tried to get it for the show! He was really psyched on it.