I don't tend to see a lot of problems with applications bugging out when QuartzGL is enabled on a modern (i.e. 10.5.6) leopard system. With 10.4, this was clearly not the case. So, if the GMA950 isn't just lying to me about supporting QGL, I figure that I'll keep it enabled, just like I do on my 'big' Mac (Penryn MBP w/ 8600M).
If anyone who wants to use QGL has a specific problem with a given application (buggy rendering, slowness, crashing), it is easy to fix this issue on 10.5.X without killing QGL system-wide. Just go into the .app bundle and edit the Info.plist file with the property list editor, so you can make a new sibling variable. Make the variable of type 'boolean,' set the default value to 'no' and then name the variable "QuartzGLEnable"--save the Info.plist file and launch the application again; QGL will be disabled for that application, but will still work for others. Apple originally planned to allow developers to opt in or out of using QGL on an app-by-app basis, but for whatever reason, they chose to shitcan QGL and ship 10.5 with it as a 'hidden' option only, instead of the system default behavior.