SAN, NAS, Cost and Benefits?

luetin asks: "Our company is at the point where our storage and backup infrastructure is ok, but not for much longer. We are looking into SAN, NAS, and variations thereof. We are a small IT department, with two sysadmins and two programmers. Right now we have stored/circulating about 2TB of data, and that's going to increase steadily in coming years. Does Slashdot have experience setting up SANs? Tales of costs and benefits of SANs versus a gaggle of NAS? Can SAN be implemented by reasonably seasoned IT people, or is it too dark an art?"