I upgraded to CS3 (from CS2) on a Dual 2.7GHz Power PC G5 - which was about as chunky as they come on the old Motorola chipset. I have maybe 20,000 images mostly in the 5-20 mb range. Bridge and Photoshop have added several excellent features including some great black and white processing, superior raw processing and a more sophisticated keywords system. They also made access to images in Bridge better through providing a keyword index and count that provides a sub-selection from a Find to or folder.
So far so good. But I also found a lot of problems with hanging, crashing and slowness (that were not there before). There were also initially problems with the Bridge search as the system needed to 'visit' the folders to create an index and this did not work properly. Some of these problems were resolved but new ones keep coming along. Whether this is because of the chipset or poor quality control or bad design I don't know, but it can be very infuriating.