Our friends at Tricycle will push through a zero-based karma system (no self-voting possible) sometime this evening. At present this will only cover future posts/comments - they may go back and revise history some time in the indefinite future (or not), but apparently that would be overly complicated for now. We'll see how this works.
Up votes aren't capped but your point about lurkers is interesting. The primary motivation for the change is to stop it being easy to just register an account then down vote everything you can find.