At the risk of sounding even more egotistical than I have been recently (difficult, I know... but I'm going to try!), I'll quote myself from an article we published over on iPodObserver regarding the iPhone App Store today:
I would love to be able to download an app and have a 24-hour trial period. If I like it, I'll buy it. If I don't, it magically disappears from my device, never to return unless I fork over the cashola.
Post your comments over at iPO, if you please -- there's already a good trail happening there and we should keep the conversation in one place.