To be honest i've got on ok with UP3 so far, it installed ok and in general runs ok.
I do the same as Jabo, and have seperate installs for different versions of IL2 and this has worked out well for me.
Currently I have UP3, 4.101 (ModAct) and good old UP2 just in case! (Plus a stock 4.101 vanilla)
However, when it comes to playing co-ops I agree that we have to fly a version that is stable for everybody, and this last week has proved that not everyone is having such a smooth time of it.
We have to remember that UP3 is still a release candidate and many of the bugs experienced are being worked on for the final release, whenever that may be!
There does seem to be a lot bugs that are affecting mission building/conversions from 4.09, which is particularly worrying.
I for one am willing to give the UP team the benefit of the doubt and continue to trial version 3, because I like what it has to offer.
BUT, I absolutely agree that for the time being we should stick with what is best for the majority, and if that is 4.101, then so be it!