I only just bought a 1.5TB drive, and noticed that the price of 2TB is falling to within consideration [though have you read some of the comments about the Western Digital My Book Essential USB 2.0, these drives seem to include some built-in software in firmware that does odd things and that you CANNOT remove? I'm not sure I want to touch those...]
Now Seagate comes along, talking up 3TB drives, which - frighteningly - no longer seems that big! Initial reports were a bit disturbing for while they said that these drives would work fine with Windows 7 (and NOT work with Windows XP) there was no mention of how they'd work with Mac OS.
Now Electronista reports that Seagate confirmed to them that Snow Leopard should work fine with these drives; and installation may be easier than Windows 7. No information on what happens if you hook these up to Mac OS Leopard...
These 3TB drives are expected later this year.
[Meanwhile, anyone looked at Seagate's new GoFlex system? Seagate FreeAgent GoFlex Ultra-Portable External Hard Drive]
Electronista: Seagate confirms Mac support for 3TB hard drive