Ext4 to be standard for Fedora 11, Btrfs also included (heise online)

The benchmarks I've seen until now (with Phoronix as the only exception, but, well, often their benchmarks are a bit 'off' and not well targeted toward what they want to measure) show similar performances; usually XFS and EXT4 are paired, in some operations one of them is faster than the other but never by significant margins. I'm going to do some limited testing on my own, but I couldn't find the time yet.

With regard to XFS reputation: you can find people complaining that the filesystem ate their data for every single filesystem out there. I've been using XFS for at least two and a half year, on two different machines; my system is pretty stable, but there were a few blackouts and I suffered many lockups when I was testing the bleeding edge X stack last year, and I never experienced data losses or filesystem corruptions.