Add me to those that upgraded to the 40D. The decision was made easier by the good price, instant rebate, and the fact that selling my used 30D and the unneeded 28-135 lens will just about fund the upgrade.

My initial impressions after just two day shooting are:
-faster reacting than the 30D
-if shooting wildlife fill up the 2 GB cards pretty quick shooting raw
-on the screen there appears to be a bit more noise than I am used to with the 30D at ISO 400. Noise did not show up in an 11 x 14 print
-AF tracks well on moving objects
-my images appear softer than they did with my 30D. I just need to check the actual accuracy of the focus and if it's ok then it must be some within my normal PP workflow.
-menu is different than with my 30D and 5D but I'm already getting used to that
-CS2 ACR does not recognize the 40D's raw files. So I have to change my RAW conversion workflow or upgrade to CS3
-shutter sounds different, maybe a bit quieter
-larger LCD is nice but still not the sharpest in the world
-the older Canon 20D/30D grip does work with it

I'm hoping the AF system serves me better when shooting BIFs, soccer games, and football games. The additional fps will help to. I was practicing with my son Friday trying to catch the soccer ball coming off his foot while doing a bicycle kick. Amazing how much the ball travels in one second and even with 6.5 fps it was pure luck to catch it right.

I also wanted the live view to help me get critical focus with all the alternative manual focus lenses I shoot. Sort of a warmup for me until the replacement for the 5D comes out.

Oh, and the 5D still gives a nicer (cleaner?) image.