It depends what you plan to put on them. If it is video or other large amounts of data then you'll need speed.

Most NAS devices are slow(er) than a USB2 or Firewire drive, unless you go with a more expensive NAS like a ReadyNAS.

I messed around with several NAS units till I ended up going with an external eSATA enclosure with 750Gb drives:

http://shop4.outpost.com/product/525...H:MAIN_RSLT_PG

I've also got 2 Seagate FreeAgent pro eSATA drives which also perform quite well.

In the end I spent abour $500 less than I would have on a ReadyNAS.

Of course, you could always go the way of building your own NAS with FreeNAS, but I'm sure Spacebass will be here soon to explain that