I prefer RAW over JPEG only because I prefer to edit in RAW, esp. in CS4's RAW editor (which cannot be used for non-RAW files such as JPEGs). I just find it easier to adjust things like fill light, clarity, vibrance, sharpness, exposure, white balance and more in CS4's RAW editor than in CS4 itself. I do 90% of my PP'ing in either CS4's RAW editor or in Canon's RAW editor, including cropping, rotating, straightening, spot touch ups, etc. It's just easier and the results, superior, IMHO.
Edited in CS4's RAW editor then converted to JPEG. The differences between my edited version and Wulf's are more evident when both are viewed at the 1024x:768 size):
Here is a sample screen shot of CS4's RAW editor: (larger photo available on flickr):
