Two off the top of my head:
-Fix "Keep Me Logged In" to actually keep you logged in until the user deletes the cookie. Current log in UI will log you out in 24h or less even if you tell the site to keep you logged in. This is only one slight step above the old EVE Online forums which would log you out so frequently it might do it before you finish posting.
-After logging in, return user to the page they were viewing before they logged in. Currently it returns you to the home page. This is very negative for forum users especially given the above problem, since if you find a thread you want to post in, realize you cant because you are not logged in, log in, go back to the home page and have to find the thread again (unless you had the foresight to copy/paste the post URL before you logged in and ffs why in 2012 should we still need to do that?)
MWO is shaping up to be a beautiful game, let's have a smooth website + forum experience to go with it. Anyone else with suggestions, post them below