there are lots of definitions of populist i think. the one i tend to go by is a politician who has no genuine beliefs, but goes by what is most popular at the time - whatever that may be.
i'm not saying that's obama, i'm just postulating where i think some of the hate may come from. i can understand feeling a lot of anger towards obama if you truly believe he is being disingenuous.
I guess that is part of populism, but more specifically a populist politician is one that portrays him/herself as "one of you". It is anti-enlist perspective and a celebration of ordinary people. Extreme cases get bogged down in conspiracy theories (an elite few control the country), but really every successful politician has to be a populist to some degree; a "I feel your pain" kind of thing. Obama's Whole Foods arugula statement was about as far from populism as you can get.
Conservatives (W for instance) and liberals (the Clintons' support among the working class) convey populist values, and to my mind that in itself is not really a problem. I suppose this issue is if it's genuine or not, does the politician really have the interests of ordinary people in mind?
When you talk about "a politician who has no genuine beliefs, but goes by what is most popular at the time", that is populism I suppose, but that is really common among brokerage systems, whether the candidate is a populist or not.