I for one like the XP system. Especially in the beginning, it's rather easy to bump up a level, which makes this whole Perl Monks deal some sort of adventure ;)

Secondly, I like it, 'cause it shows what nodes of yours are considered "usefull" to other monks. I like to see a node with a lot of ++ votes, 'cause then I can think that I actually gave some decent reply (too bad I barely receive ++ votes ;)

Donwvoting happens for numerous reasons. From plain "this reply does not make sense at all" to "oh well, sorry, I hit the wrong button", or even "I don't like this person". If someone is about to downvote you for dubious reasons, the chances are pretty slim (s)he is going to explain why (s)he downvoted the node. And honestly, I'd rather not get a /msg saying "I don't like you, so I downvoted #node" ;) If a node gets downvoted because of a valid reason, it's easy to spot, because someone will reply to it, or you can read other replies (indicating a different solution to the problem).

... just my 2 euro cents