I think some youtube videos of people in "actual" situations would be legit. Using ideas already posted in this thread would work fine.

Like two guys driving in a car, and one guy pulls out his iphone and starts playing some crap music. Then the other guy pulls out his n900, and FM transmits some good music to cover it up. And the iphone guy is like dude, how are you doing that!!!

Or (my favorite part of the tablets):

The iPhone guy is like 'OHHH LOOOK! A app to take timed pictures! Only $5!' I'm a downloading it!!

Then the n900 guy is like "pshhh..." Whips out his tablet, and writes a shell script in the time it takes for the app to download.

However, the biggest selling point of the N900 is the multitasking, so something like a guy browsing the web, and listing to music, and talking on IM, while downloading some torrents, while doing other stuff i cant think off...