The 550D arrived at work today, and I'm impressed by the image quality. Fine jpegs run to 6 meg, and raw to 23 meg. It will work with the new SDXC card if you can find/afford one as an SDHC soon fills shooting RAW + JPEG. A laptop screen with the images resized to 600 *400 just doesn't do justice to the pictures, on the 27" iMac the detail is amazing.
The only issues I have with it are:
1. Different battery to 1000/450/500D, so will need a new battery grip.
2. Release price, typical Canon (I hope) twice what it will be in a few months.