We upgraded but beware, we had to go back to 2.5 appe, because of a bug with drop shadows that rendered as solid blocks, we decided to go back to the older verison to avoid anymore surprises, if you would like to try the file through your own RIP, PM me and ill send it to you, it gave us a bit of a shock because we run the same job every month and the designer didnt even really look at the drop shadows on the raster email proof because it was always fine before.
As for the client working better on the G5, what do you mean by "snappier", it doesnt crash? we have always used the PC client which has always been snappier than the mac version, I gave up using the mac version after it crashed the 3rd time, mind you, I am sick of trying to keep up to date with OSX versioning, how many tigers and leopards can they keep killing, the PC is much easier and has only crashed once or twice out of a 1000, so I wouldnt point the finger at XMF, that would almost certainly be an apple software issue, we have never had a problem with stability using the PC clients and one of the machines I use for remote desktop is pretty old and nasty but still doesnt crash.
It is still a great workflow, but this new version was a dissapointment for a 2.5 to 3.0 size change, should have been called 2.6.