i have a wide variety of these, from c up to cs5 and i continue to revert back to cs2 as i am more familar with the interface and will use the other version for specific tools that are not found on cs2.
How much and how well do you use photoshop? Learning a whole new system may or maynot be worth your time? At least 5 will have features that you have been using.
why not download the free trials of both and test them out and go with what feels the best for your workflow?
CS5 has some great enhancements in it. The noise reduction has been nicely upped amongst other things.
Dont buy into the "get LightRoom 3" thing. Its a good software, but if you are used to photoshop, stick with it. The bridge software is pretty much as powerful in terms of image manipulation as lightroom 3...same sliders, more or less same workflow. It is missing the file sorting and structure LR3 has, but it can give you what you want for quick multiple edits, staying with Photoshop for the heavier work.