It was fun to play with the video, but having to move the mode dial to video was an irritant. Especially because there were so many settings between PASM and movie mode (scenes and CA), so you really had to look at the camera to move back and forth. A dedicated video button would have been a help.
Personally, I'm not sure I like movie mode on these DSLRs, as you use live view, which means you're holding a large-ish camera out in front of you, and it's unstable. Also, AF in Live View is slow, so it's better to go MF, and the live view screen is not great for MF in full day light. But that's not a knock on the T1i itself, but for most video DSLRs.
What I REALLY didn't like in the T1i was the stills controls. In my XTi there are five "thumb" buttons (four in a circle and the set button in the middle) from which I could access ISO, WB, AF mode, metering mode and use set for flash compensation, all right at my thumb.
The T1i isn't like that. ISO is now behind the shutter and (for me) ergonomically uncomfortable to access. It may be different for others.
Additionally, they've added "picture styles" (natural, vivid, etc. -- a jpg setting) and burst mode to the four buttons in a circle -- meaning you have to leave out either flash compensation or exposure compensation from your thumb settings, and instead access one or the other from the menus section.
For me, I lost my common settings, with ISO going to an inconvenient location (for my hands) and losing one of the compensation settings in favor of a jpg setting.
Also, I really like having the "play" button for review on the left side. Hold the camera in my right hand, and flip through shots with my left. This re-arrangement of buttons was done to make room for the larger LCD, so that's just trade-off.
I didn't see any appreciable up-tick in IQ over my XTi in RAW (not sure about jpg).