Mutliplayer EXP Hacking?
Anyway to modify exp levels or is it server sided?
It's server sided in bukkit.
Stored in player configs I believe
Don't think there is a way for that but if you have the correct permissions type this:
/xp (playername) (amount)
Or the Bottle O Enchanting works
You can't. Anything inventory is server side. However, me and a friend are looking into meta data exploits. I doubt we'll find something useful on bukkit but it'll be fun to see if it's possible on vanilla.