For those of you that might not be aware: you can download a fully-functional trial of CS5 from the Adobe site. Playing around with it may help you decide if it's worth it.

I'm toying around with PS CS5 now, but have not toyed around with many new features. The only initial difference I have noticed from CS4 is draw times seem to be improved on my setup (GTX 275 working with large PSB files) but everything else (filters, etc.) seems a little more sluggish (only very slightly). I also need to adjust the zoom tool; it defaults to a setup where clicking and dragging produces some sort of dynamic zoom, instead of the traditional marquee zoom.

With regard to Eyecandy, my expectation would be that old versions would continue to work with 32-bit Photoshop versions, but not 64-bit. So unless you like switching back and forth between PS versions, you have to choose between having access to your old filter and being able to utilize more RAM for your images. I really wish Adobe would come up with something that would enable 32-bit brushes in 64-bit PS.