I used to use an aged eMac as a server in my room. I recently replace this eMac with a Synology DS-207. I sold my eMac for 700. I got my Synology for 1400 in a garage sales and an extra 160G HD for 300. The synology saved a lot of space and it is very quiet. Well, not as silent as in library but at least less noisy than the CRT monitor in the eMac. The synology do Samba, printer sharing and Bit torrent.
The power consumption of my server is drastically reduced from 240W to 34W.
I got my Synology for HKD 1700, minus 700 from selling the eMac. I actually paid $1000.
The energy saved is 240W - 34W = 206 W.
Amount of time I need to get back $1000 from the power bill (t):
Money / unit price of 1 KWH of electricity from CLP = Power (in KW) * t (in Hour)
1000/0.9 = 206/1000 * t
1111.111 / 0.206 = t
5393 = t
5393 hours = 225 days = 7.5 month = 0.62 years
I think it is a valuable investment. It is "Green" as well.