Ok, ok, I admit it.  I've been using Photoshop 5.5 for close to eight years now.  It's fast and light; it works well with my Wacom tablet and dual-core cpu and it has been a great work-horse for both personal and professional projects for a long time.  That said, I've been playing with a trial version of CS3 and from what I can see... it's just Photoshop... but it takes much longer to load than my old favorite.  I still don't have a solid reason to upgrade because 5.5 does everything I want it to do and it does them well, EXCEPT it lacks the ability to use ABR custom brush sets.  

I've read about CS versions being resource hogs and a lot of CS/2 reviews said they wished they hadn't upgraded from 7.  Can any CS users convince me to shell out the cash?  Are there any features CS has that you "can't live without" now that you've used it for a while?   Is it really worth it just to gain the ability to use those cool brush sets?

Any thoughts or advice would be appreciated.