Regarding RAW vs. JPEG, I shoot in RAW at all times. The flexibility you get in terms of post-processing is fantastic. I've used both the Canon Digital Pro software that is bundled with the camera, and Adobe Photoshop CS's Camera RAW plug-in, which now supports the 20D. I primarily use Photoshop today, since that's where I end up doing all of my retouching, etc.

For 2nd-curtain flash sync, the answer is yes with the new Canon Speedlite 580EX as well as the 550EX. I'm not sure about other flash units.