Thanks to Baseball-Reference.com's milestones page, we can see which players have a shot at major career milestones in 2012.
Ivan Rodriguez and Omar Vizquel both need about 150 hits to reach 3,000. It seems unlikely that either will get it, in 2012 or beyond.
Paul Konerko needs just 4 homers for 400. Vladimir Guerrero is 1 homer from 450 and Albert Pujols is 5 from the same mark. Unless one of those guys puts up a monster season, nobody will reach 500 homers in 2012.
Manny Ramirez needs 174 total bases to be the 20th player to reach 5000. I'll go ahead and bet against this happening.
If Alex Rodriguez can get 103 RBI, he'll pass Barry Bonds for 4th all-time behind just Hank Aaron, Babe Ruth, and Cap Anson.
Jose Reyes' next triple will give him 100. The only 3 active players with that many are Jimmy Rollins, Johnny Damon, and Carl Crawford.
Jim Thome is 110 strikeouts behind Reggie Jackson for 1st all-time. I bet that he will never pass Jackson, though.
Roy Halladay needs 12 wins for 200. Tim Wakefield is the winningest active pitcher and he has 200 exactly. We aren't going to see another 300-game winner for a long time--at least 5 years, probably at least 7 or 8.
Livan Hernandez has the most starts of any active pitcher and needs 26 more starts for 500.