Update: Discovered something interesting about the aspect ratio... hint: it's not 16:9.
A new "Rented Movies" directory shows up in our iTunes library. Clicking "More Info" gives you some more information about your rental. The expiration time appears in the upper-right corner. The 24-hour viewing clock is already ticking since we started watching the film during download. Really, who can wait the 30 day maximum before watching a film they just rented?
Don't worry, Apple is happy to nag you about your rentals.
Damn, have to run out. Let's try to transfer the rental to our iPod like Steve showed us during the keynote.
iPod plugged in, ready to sync and... er, what's this? How come our Video tab looks nothing like Steve's? Oh right, the rental transfers to iPods are for current generation "iPod classic, iPod nano with video and iPod touch models" only. Where's the firmware love Apple? Our iPod is only one generation old!

After locating the file on our hard drive (~/Music/iTunes/iTunes Music/Movies) we discover some interesting details about our download. So what aspect ratio is 853 x 356 pixel exactly? 16:9, 4:3, or some iphone proprietary ratio sitting in between? None of the above. It's actually a cinematic 2.39:1.

Conclusion
Despite the few quirks we experienced, the steps required to rent from iTunes were dead simple and the ability to play the movie after just a few minutes of clicking "rent movie" was a big plus for our Type A personalities. Assuming you have the bandwidth that is. Sure, we're not talking HD video or 5.1 audio here. Nevertheless, the quality was surprisingly good when displayed full-screen on our 30-inch, 2560 x 1600 pixel display -- even when sitting at keyboard-length from the monitor.
Perhaps the most telling result of our experience is this: we're tempted to rent again, soon.
So yeah, we rented a second flick -- Zoolander. Note the variation in pixel density which also results in a 2.35:1 aspect ratio. Looks like iTunes renters are in for a crapshoot.

Oh, and in case you're wondering, yes we tried to open the file with VLC and other media players. No luck, the file is locked down tight with Apple's own flavor of special DRM sauce. You can see a few individual frames of the film but no video. iTunes is the only capable player.
Conclusion
Despite the few quirks we experienced, the steps required to rent from iTunes were dead simple and the ability to play the movie after just a few minutes of clicking "rent movie" was a big plus for our Type A personalities. Assuming you have the bandwidth that is. Sure, we're not talking HD video or 5.1 audio here. Nevertheless, the quality was surprisingly good when displayed full-screen on our 30-inch, 2560 x 1600 pixel display -- even when sitting at keyboard-length from the monitor.
Perhaps the most telling result of our experience is this: we're tempted to rent again, soon.