I have a Canon T1i and it seems to be working just fine, but I shoot raw and Adobe doesn't have a Camera Raw that will recognize my shots. They told me to transfer the shots to another Rebel (I do have an XSi) and then use the version of CR that's available now. That doesn't make sense to me. The shots were taken with the new camera, so how is the other camera going to do anything to the SD card to make the shots open in Camera Raw? Bridge no longer allows me to switch to CR since I just upgraded to their newest version. I know, I know, you think I'm a real newbie, but I'm not.
I don't know when, but Adobe have said that the T1i will be supported in the next version of ACR (which I think will be 5.4?). You will then need to be running Photoshop CS4, since CS3 won't support ACR past version 4.6.
These (and many other) reasons are why I use the Canon DPP RAW converter which works very well and is supplied free with all Canon DSLRs. Obviously the version shipping with the T1i will convert T1i RAW files. I'm using DPP 126.96.36.199 and it works fine with T1i RAW files.
I have no idea how transfering shots from a T1i to an XSi is supposed to make them readable by older versions of ACR