I just spent about five hours this weekend experimenting with Titanium Mobile and for someone like me knows Javascript, but not Objective-C or Cocoa, it looks awesome. After spending some time trying to get kick started using Objective-C, Cocoa, Interface Builder and XCode, I would guess that Titanium might reduce the time it would take me to build a substantial iPhone app by maybe 5-10X.

pekpongpaet and chadpaulson used it to win the iPhone hackathon competition at this past weekend's Day of Mobile. Chad claims he'll write a post about it, but if he doesn't, the tl;dr is that it made him a believer.