You don't have to like a person, you don't have to agree with them.
But what you do have to remember is that there are things that a president knows that the rest of us don't know. Decisions are based on things that we don't have the complete facts to, and the same will happen with Obama, I will probably agree with him less than I did Bush, but he is, not by my choice or vote, the president.
I am very upset that Bush was booed at the inaguration, he deserves more respect for that, if I have something to say to a person, I will say it to them to their face, I don't think that tactics like that are appropriate, just like the journalist how threw his shoes at Bush, there are better ways.
Sure I voice negative Opinions about Obama as a person, but you know what, I have emailed him those very same opinions, whether he has read or seen them, I don't know, but I have no problem telling him what I think of him.
And if you have a beef with President Bush, then you should find a way to say it to him privately as well as publicly.