thats a really general question...
What apps from CS do you use? What do you use them for?
I would argue being a designer as well as dabbling in 3d that the new features in PS and AI alone warrant an upgrade. I have been waiting on multiple artboards and transparency in gradients for so long it isn't even funny.
The blob brush is ***** brilliant especially with a wacom.
The scaling and 3d features in photoshop make it worthwhile to me.
The new interface options and animation enhancments in flash make it by far a good upgrade.
I can't speak for indesign yet, haven't done any heavy duty print lately.
I use final cut, so can't speak to premier.
Also, haven't gotten into dreamweaver yet, and more than likely won't touch fireworks unless i have to for a client.
hope that helps.