Most xorg devs aren't a big fan of pbuffers but they are part of the GLX 1.3 spec which drivers want to support these days. Some drivers are considering to just fail on pbuffer creation. Encourage them to offer pbuffer support on some visuals/fbconfigs. A lot of windows apps rely on their presence including Wow in opengl32 mode and lots of other (older) programs.
Can we emulate pbuffers via FBOs, or are there some problems? Pbuffer support is troublesome on MacOS and the ATI binary driver as well, so even if the xorg devs implement it we'll be stuck with a partial fix only
In theory you might be able to offer this emulation but I think it will be very tricky and it might not work well at all. Remember pbuffers are WGL things while FBOs require a GLX/WGL context. You would have to override a bunch of GL calls, states .. I don't think this works well. Second WGL allows you to query the capabilities of a pbuffer, we would have to fake most settings which might not result in optimal performance (e.g. color bits, stencil ..).
Mainly overriding stuff and the requirement of a GLX/WGL context is problematic I think. I fear a half baked implementation which works for some of the easier apps. The drivers could also emulate pbuffers using FBOs and they might have less issues.
Roderick