Doc,
you can store as many registrations as you wish, provided you have an hard-disk or a USB stick (Regs don't take up much memory).
What Gary was saying is that Yamaha subdivides the registrations themselves in banks of eight; I use this feature to group together all the registrations referring to the same song. So, for example, you can have a registration for the first part of the song, another for the chorus, a third one for the bridge, etc.
It's actually a handy feature, and when I play another keyboard I really miss it.