Netbeans 6 and 6.1 on the same machine.. Possible..?

It must be good enough for them to think of it as a stable release. Personally, I don’t see why you would want both versions on it. If you’re worried about the possibility of something in 6.1 being buggy, despite the weeks, if not months of beta testing, then don’t use it, use 6.0 instead. If you want to contribute back to the world in a good manner, use 6.1, run across a bug and report it. That’ll improve the product and it’ll be better for you and everyone involved.