SAN FRANCISCO (MarketWatch) -- These days, many of us leave the myriad, line-by-line tax decisions to our professional preparer or the mystery men behind our tax software. But given the increasing complexity and ever-changing nature of the U.S. tax code, it makes sense to keep abreast of some of the most valuable perks yourself. After all, it doesn't hurt to make sure your software program is steering you in the right direction or to check in with your preparer to see whether you qualify for a tax break. "I'm blown away by all the changes," said Michelle Maton, an enrolled...