Picking up the various artifact pieces will grant one skill up (three per dig site) until Archaeology level 50.
http://www.wow-professions.com/wowguides/wow-archaeology-guide.html <- this site says the same thing.
I started at 130 skill, and will hit 300 here soon. I've done nothing but Dig Up stuff. I do remember when I started my Monk and Archaeology that skill ups did stop at 50. I decided to hold off on professions until I was lv90 with flying, so now I'm back at it. It has only taken me 1.5 hours to gain the 170 points so far.
Bug? or did I miss the change in notes?