I just returned my X-Fi. It works great in games, off loads the CPU nicely. Zero linux support, music with guitars sound distorted if the 24.bit crystalizer is on. So if I turn the 24.bit crystalizer off, I'm basically making it sound like my onboard audio. I don't play games that much, I'm in SUSE more than I play games. So for me it wasn't worth it...
AMD X2 4400
2GB OCZ Platinum
Caviar 320GB SATA2
SUSE 10.0 64Bit-WindowsXP x64-Vista 5270 64Bit