I'm using 3.6.13 for the Mac. No IE available anymore, and Safari pissed me off because it has only one search engine in the bar, "McGoogle", which I refuse to use. I have Ixquick as my default Search Engine on FF. I do miss the pop-up editor that Mozilla had.
Yes, but I didn't upgrade because it requires OS 10.5 or higher and I have OS 10.4.11 and no intention of buying the upgrade for this machine - which will not be supported at all when Lion is released.
The current iteration of OS X is fine. The intitial release of Lion will be quickly upgraded to 10.7.x so I'd wait a while and then buy an upgrade after about 6 months - by then most of the bigger bugs will be found and patched. While an Apple OS release is never as buggy as Microsloth it is a big OS and no doubt there will be some problems.