Can't rep anyone on the last three pages. Can't be bothered to look back further, but I'm 99% sure it's the same across the board.
You can give unlimited rep, but not all at once. You have to 'spreading love,' so to speak. Also, only so much per day. Not sure how much, though.
You are such a whore now. I've only got three bars! You must having been selling yourself a lot lately! EDIT: Just given you some more rep!
Given you some rep! It's that little star below where you post. You can 'Approve' or 'Disapprove' people's posts. You can check how much rep you have by clicking the 'Control Panel' icon next to the 'Log Out' icon.