UPGRADES:
lots of the followers wear a particular armor type only, regardless of upgrade. Lydia is heavy armor, and I found upgrading Lydia required taking the old pieces to guarantee she'd put it on. I also found she wouldn't equip it until I told her I needed her for something.
I still have a glitch though, I found a post out here that said every time we trade to them they get an invisible item that adds to their weight, so that eventually they are "full" and cannot equip or accept new gear. Was supposed to be fixed and I'm waiting until I don't have to use the console commands to do it for myself. My Lydia is still incapable of accepting a new ring, it's too heavy.
LAGS BEHIND:
Try taking a Fire Thrall with you anywhere. LOL... she's up around a corner and a mile behind me and will also pick fights and get herself killed when I can't even see what's going on. I literally have to run back sometimes and FIND her. I've found they always catch up when you go through the next instance gate of the dungeon, and that if you go find them they stay closer for awhile. Tedious and still manages to work.
It's nice they're not right there in combat getting hammered by me because they aren't sure how to stay out of the way, is a pain in the neck to have to remind our companions and followers that there's a reason they're with us and it's not so they can meander about lost in the dark a mile behind us in a cave.
