I like him, but I personally don't feel like he deserved to win any of the years he was up for it. And I don't think he deserves it over Chiwetel or McConaughey this year, either.
Yeah, I love Leo as an actor, but he hasn't had one absolutely incredible performance that really has me feeling like he's ever been snubbed. His best performances to me are in Gilbert Grape, Django and Wolf.
With Grape, he was better than the winner, (Tommy Lee Jones in The Fugitive), but he wasn;t the most deserving of the award. Ralph Fiennes should have won for Schindler's list that year. It's a snub of Ralph, not Leo.
Last year, Tommy Lee Jones, Phillip Seymour Hoffman, Christoph Waltz were all very worthy of the award and I can't argue against Waltz. I think Leo got snubbed a nomination that year with Django, but not a win. He was certainly not the clear cut best supporting actor that year.
Now with Wolf, its a huge year for lead actors, with Ejiofor, Joaquin, Dern, Redford, Hanks,and Mcconaughey, giving incredible performances. I think Belfort is DiCaprio's best performance, but again, its such a strong year, I wouldn't consider it a snub if he doesn't win.