1) When newbies first see the karma system they begin (like in any game) to work hard to raise their numbers. They watch closely to learn what kinds of comments will get them points. Ways to address this: -Make new users read the guidelines and address this issue more directly there. -Make Karma look less like a competition.
2) Like other comments have said, figuring out who upvotes bad comments requires data-mining. A serious question here is whether democracy is a viable option any longer. What is the site meant to be: a mob, or a tight community which a mob may watch? Do we educate the problem-voters, or do we dis-empower them?