We're at a point where server virtualization is really becoming pervasive. I've seen very few technologies have the kind of impact that server virtualization is having on the market today, and I see no end in sight. Everybody is adopting server virtualization regardless of geography or company size, so it's a very important issue. And server virtualization actually drives people to take storage that was otherwise internal or direct attached and network it. It doesn't make much sense to keep storage inside servers with a lot of virtual servers on them. It's like owning a TV but only watching DVDs and foregoing cable, you just lose a lot of the value.
Check out the entire NAS FAQ guide.