I crafted a rare helm that gave me 4 abilities (none that great), and an empty socket. I slotted the gem and I saw no difference. I don't recall all the stats the gem had, but I remember it having 6 dex, which doesn't show up.

Edit: NM. I found another gem and noticed that the stats are different (and rather horrible) for helms.
Edited by Shai#1275 on 5/19/2012 6:12 PM PDT