After years of buying hard drives that say 400gb, but format out to 372.529gb, Seagate lost a class-action suit that accused hard drive manufacturers of using misleading statements about the capacity of their hard drives. Hard drives have traditionally used 1,000,000,000 (1 billion) bytes for 1 gigabyte, but everyone else uses 1,073,741,824 bytes = 1 gigabyte. The difference comes from using the next power of 2 (2^30 = 1 gigabyte) vs actual byte count (1 billion bytes = 1 gigabyte). All other computer components (i.e. memory) use the power of 2 notation; looks like HD manufacturers will need to start doing that now too.
But the good part is that you can cash in (or at least help the lawyers cash in). Go to this online form and fill it out if you’ve bought a hard drive before January 1, 2006.