In this blog post, Alex Deucher writes about his GNOME Shell experience as his primary Linux UI. He lists 11 problems he's having on this new version of GNOME. The list includes lack of multiple application instances, no restart/shutdown/hibernate options, suspend on lid events, minimize controls, quick launching, system settings, and the lack of applets, among others.
As talked about in How Unity, Compiz, GNOME Shell & KWin Affect Performance, the new desktops / compositing window managers also tend to possess a lot of bugs. The GNOME Shell is also in a position where if using it while gaming, you'll be at a performance loss compared to the other options.
Related to the GNOME Shell and graphics drivers, David Airlie pushed a new R600g commit that adds context control to the start of command submission. He reports this should at least let "GNOME Shell run for a while longer."
In the forums you can share your current Linux desktop experiences.