As Russ points out in his earlier re2-related blog posts, these regex engines still perform non-linearly on inputs which don't involve look-around, look-behind, etc. There's plenty of room for improvement even if they want to keep these features.
No, they don't. Be wary. I tried to use btrfs in raid10 (data and metadata) mode for my latest array of large disks (4x 2TB WD Caviar Blacks); 70 GB in copying data from my old md array, I got a kernel OOPS. This was with very recent btrfs code -- Fedora 16 with a 3.1.x kernel and btrfs-progs-0.19-16.fc16. It's simply not ready.