A better indicator would be a "Likely voter" poll. That type factors in actual voting patterns. In CA Republicans are more likely to vote than Democrats - this tends to balance out the Democrats registration edge. Congressional, State Assembly, and State Senate districts that are not at least +5% Democrat registration advantage are considered "in play" for Republicans.
There are two other key points for this Gubinatorial election. The Green Party candidate is polling about 5% of the vote when listed in to poll questionaire. Almost all of that liberal vote is pulled from the Davis column. Will these voters stay Green? Or will the bleed back to Davis (like Nader voters to Gore in the last Presidential election)? The other key point is the illegal/dead vote which greatly favors the Democrats. They have put a lot of money and effort into registering as many ineligible voters as possible. Also, the big, Democrat-dominated counties (such as Los Angeles and San Francisco) are way behind in cleaning up their voter polls. Hence, "standing absentee ballots" are sent to addresses of former residents, and are illegally voted by the current residents. Also, illegal aliens, mostly Mexican, vote in heavily Hispanic districts. (This is how Loretta Sanchez beat Robert Doren a few years ago.)
IMHO, Simon will not be safe from voter fraud unless he is up 10 points.