And so far its been pretty good with one exception. Mame stopped working. Now previously I had been using SDL Mame as this was the only one I found that displayed correctly, although sound wasn't working. Now, using the GMAMEUI it wasn't running the executable as all, with an odd byte order error.
Turns out (I think) that SDL mame has been merged with normal Mame, so by uninstalling SDL, ensuring basic Mame was installed, and pointing GMAMEUI to the Mame executable, it all started working. And I do mean ALL - the sounds as well. Hurrah!
The only other issue with 10.10 I have found is that F-Spot Import seems to be very very slow. Will post when I figure that one out.