I have to 2.6 running on one of my non-critical machines. The speed increase is absolutely amazing, at least for my uses. The most significant increase though is probably with the GUI and pre-empt, which can be applied to 2.4. Right now the only thing I lost are USB and Sound. Both are fairly trivial to fix, but I haven't had a need to do so yet. I would agree though that unless you know what your doing, don't go for it. In case noone has noticed, Fedora released Core 2 test 1 today (it has 2.6)

Start downloading and submit those bug reports everyone!
Regards,
Steve