I've had wildcats and oxygens and my friends mostly have nvidia cards, the crashes do seem hardware related.
Using Wildcat crashed alomost never with Houdini, a fair amount in XSI, every few days or for certain tasks in XSI almost always(whos to blame there?) but crashed most in Maya but not the almost guaranteed crashes of XSI for certain tasks, especially render region.
Using Oxygen XSI used to crash a lot more, Maya was OK and Houdini was OK excpet in Dual screen where its useable unless you maximize an OGL window on the extended monitor then you're guaranteed a crash.
Comparing XSI and Maya for stability I'd have to say now that XSI has worked out most of the bugs from v1 and it is very stable, more stable than Maya by a bit , but ver 2 that just came out may bring a whole new set of problems.