as far as I know if you install Windows 8 on the SAME computer you originally had W7 on (or even XP) where you activated Office 2010 - activation should cause NO problems --and won't count in the number of activations if you go back to W7 (or even XP).
Actually the strange thing is I never even got asked to activate office 2010 but it did ask me before installing it to enter the product key and I had to wait while this was verified before the install could continue.
If you DO run into problems activate by phone -- Ms won't give you ANY hassles if you are saying you are testing Office 2010 on W8 development preview.
Enterprise versions (Office 2007) and terminal services product key for 2010 are legal multiple activations so won't cause a problem anyway.
Just posted this in case people want to try Office (2007 / 2010) on W8 but are worried about losing activation status if they decide to go back to their original OS (XP / W7 ). I've left out VISTA as I don't think many can still be using this anymore.