Before anyone goes nuts -- please understand this is beta, not the finished product, and ArenaNet still has months to optimize the hardware problems. Nvidia nor AMD have released drivers optimized for GW2 either, and probably won't until near the game's release.
According to these notes the game is currently very CPU-bound (not a huge surprise, WoW is too); overclocking your CPU/GPU could hinder performance (this one is the strangest to me); and SLI unsupported (again, not surprising for a beta), but I'm sure these technical issues will be resolved before release. ArenaNet has spent several years working on this game and they're unlikely to release such a dedicated and polished game without fixing these significant optimization issues.
Edited by velocd - 4/24/12 at 11:36pm