I'm probably going to skip it.
It may sound silly, but I want Illustrator and InDesign in 64-bit as well. I use Illustrator a lot for ads and projects that involve photography, and when you have lots of photos linked in Illustrator, the program slows tremendously. Heck, it even slows when you have lots of layers (I'll sometimes have around 20 or more layers with gradient/pattern fills and such). I can't see upgrading unless I can utilize more than just 3GB or so of RAM and multi-core processors.
I don't care too much about extra tool features because in practice, I just don't use them all that much. What I care about is pure performance, and CS5 doesn't appear to have much for me in that regard (again, strictly referring to Illustrator and InDesign). I'm not going to shell out $600 (Design Premium upgrade) just for new brush models, perspective guides, and other silly things I won't use.
For the record, I've only had CS4 for about 14 months, and other than performance issues mentioned above, I have no issues with it at all. In short, there's no compelling reason for me to upgrade.