I don't know much about them other than a snippet I heard from a podcast on the WD red drives, but the rundown was that the red drives had a TLER that was better suited for RAID arrays (green drives sometimes drop out of the RAID array apparently?). I run WHS myself (the older one) so I dont use RAID, thus, I bought the green drives.
Also, you get an extra year of warranty on the red drive vs the green drive (3 years vs 2 years).
The price, normally, is supposed to be $10 extra on a 2tb drive (120 vs 130) for the red, but right now the green is $20 off on newegg. That makes the spread $30, or 30%.
For close to the same cash with the sale on the greens, I'd rather have 4 2TB green drives than 3 2TB red drives, but comparing normal prices I'd go with the red.