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.
Some people were testing the system by deliberately not voting for themselves. Also, Reddit doesn't really run off a proper database. And there could be other consistency checks (I haven't looked at the code).
Last I spoke with Steve Huffman, he told me they were running on top of PostgreSQL, but maybe they switched to something non-relational in the most recent rewrite. Now you've got me curious; I'll check the source.