Everything within the CS5.5 suite would run under a single serial number, the one for MC that you received... The other keys would be for the separate 32-bit CS4 versions of AE and PP. And you can use all of them on up to two of your computers.
Lastly, you don't have to uninstall CS3 if you don't want to - it can run it side-by-side with CS4/CS5 if that helps, or you could uninstall it if you like. If you do remove it, you might want to use the Creative Suite Cleaner Tool afterwards, just in case.
Hope this answers all your questions - if not, just post back!
Great, and thanks for the quick reply! I also bought the Total Training DVD set so I'm not totally fumbling my way through like I've been doing with CS3.
Is there any advantage to leaving CS3 on the computer? I don't think I have any files that will only open with CS3...unless InDesign projects are that way (but I should probably re-create them in CS5.5 anyway since I made them without any of the slick automation like page numbering, table of contents, etc.--I've been manually editing those).
Sure. Well, there are really only two reasons that folks might leave an older version on their system:
1. For comfort and familiarity while coming up to speed on the new release.
2. For saving back and managing older file formats if necessary in your work.
But, if neither of those apply to you, there's no particular advantage.
Enjoy the new release!
Thanks again for the quick and helpful reply. I plan on totally jettisoning CS3, using the Cleaner Tool to remove all traces, and plunge headfirst into CS5.5. I primarily use it for some volunteer work with a couple of non-profit orgs and the next due-out isn't until December, so I have some time to get acquainted with CS5.5.