» Sat Jun 09, 2012 8:15 pm
Here's some basic info on followers. I also included the link, which lists more info, and also a link to a Google excel-type spreadsheet.
A follower's skills, health, and other stats are set when they are first created (which is typically when you enter their starting cell, become a Thane, and so on) and never improve from that point, outside of a handful of special cases. Each follower has a maximum level (which varies for each), and a specific set of favored skills, which are dictated by their http://www.uesp.net/wiki/Skyrim:Classes.
http://www.uesp.net/wiki/Skyrim:Followers
This also explains why, when you give a follower a certain type weapon, they may/may not use it, or at least not as often as you like.