Yes I know you can configure a PC to be a server. I've been running WHS for a few years now and it's OK. I think this NAS I'm talking about might actually be better. While not having the processing power, it's configured to do lots.

Mail Server
Web Server
File Server (with Mac OS X support)
Print Server
I-Tunes
DNLA Server
etc. etc.

There's some great stuff under the hood. As for saving the landfill you make a good point. But think about how much power is consumed by your server box vs. this NAS. I haven't done any calculations but considering it powers down and/or sleeps when not in use I think makes it a compelling choice to save on power.

I'm considering killing my WHS server box and going the NAS route.