Chris,
Great question. For production we never recommend Milestone releases (always Beta, we never release Alpha because it's hardly usable), but that doesn't stop our early adopters
There are quirks in 7.0 so far that are percolating up from Ganymede, that is one of the reasons we pushed our 7.0 GA release out, so we could pick up the 3.4.1 patch release from Ganymede in the process and have a more stable experience for everyone.
While there are some quirks, we didn't come across any full breaks of functionality. What I would suggest is doing a dual-install of MyEclipse 6.5 and 7.0, side by side (in different directories) and you can go ahead and fall back to 6.5 if you run into some snags in 7.0 that are show-stoppers. Otherwise it should be smooth sailing for you.