I have an 8-core 3GHz Mac Pro with 5GB of RAM (still planning on upgrading to maybe 8GB or so), so I think I'll be fine.
All totaled I probably have close to 3TB of storage, but it's across multiple locations (actually in the Mac Pro, a file server and external hard drives)... I have 1TB worth in a mirrored RAID already, but I'd love to get a Drobo or something else with a solid RAID setup and throw some 1TB drives in solely for photo storage.
As much as I hate to "waste" the 21MP of the 5D Mark II, I think I'll probably also shoot in sRAW for most random shooting, only bumping to 21MP for more special occasions.. but that also depends on how big those 21MP RAW files end up being, too...