Here's a few things. He certainly is NOT conservative. In fact, I'm surprised he's a registered Republican:
This year, he authored a bill to increase the minimum wage. When he couldn't get any support from Republican legislators, he pushed to resurrect the previously dormant Industrial Welfare Commission (with Schwarzenegger's help) to avoid a vote by the legislature altogether. He broke party lines in July 2003 on a crucial vote, helping to undermine the Republican fiscal recovery plan designed to avoid the financial crisis.
In 2001, he co-authored AB 540, with leftist Marco Firebaugh, legislation that gave in-state tuition status to illegal immigrants.
In 2001, he pushed a $500,000 earmark in the budget for the "Abel Maldonado Youth Center"
He broke party lines in 1999, voting for an assault weapon ban publicly stating "They are weapons of war." and "they shouldn't be on the streets," statements used by the Democrats to strengthen their campaign (which succeeded).
The above (post 26) is a summary of news articles I read yesterday.
Excerpts and citations were posted on this thread (See posts 30-35).
There is also some question about his claiming an endorsement from the phantom "California Republican Taxpayers Association," a new, unapproved group that apparently only exists to endorse Abel. (See here.)
Fweh! I just remember him as the 26-year old mayor of Santa Maria, then Assemblyman when he traveled the state with W during the 2000 presidential election. I'm ashamed to say I haven't followed how he's voted.