My husband and I are having a weird, semi-similar issue... We have the exact same new machines, except he has Win8 64bit on it and I'm on Win7 Ultimat 64bit. We could both play fine during the betas, but since the game has gone live, my husband's game constantly freezes... There's no BSOD and he can tab out and do other things, but the game is frozen and he has to force close it and log back in. There's been no real pattern as to when it happens.
A while back that was "the end" of the gaming evening because the game kept insisting he was still logged in (and I would still see his toon standing where he crashed). Now it at least lets him log back in relatively quickly (except when the server full message pops up), but this happens sometimes 6 times within 30 minutes, and then he no longer feels like playing (understandably).
I have had absolutely no problems *knock on wood*, and I've not found anything online to indicate that there's a Win8-FFxiv issue or any Win8 specific hardware driver issues, but it's literally the only difference between our machines. Drivers are up-to-date, both have no temperature issues, no issues with other games or programs. I have him try things that people suggest on the forums, but so far nothing has worked :(
I hope someone (preferably SE :P) comes up with a good solid fix soon for whatever this stuff is *sigh*