1.8 is out in sneaky peek form already, but is static at the moment as all development resources seem to be focused on the iPad launch. I'm not aware of any reason why you can't switch back and forth between 1.7.5 and 1.8 -- no file format changes, for example.

I have noticed that the frequency of duplicate projects has dropped with 1.8, but there might still be some corner case yet unfixed, as I've gotten one or two.