It's not so difficult to beat Houdini in correspondence chess. Computers still lack certain elements of positional understanding, and they can certainly be outplayed by a strong player. On rapid/blitz games though, it is a totally different story.
I'd be kind of surprised if humans do better in correspondence chess against a computer than in a 'normal' timed (but not rapid/blitz) game, because it can spend every second calculating (unless restricted in some way) whereas a human has the matter of life to attend to.
The Houdini chess engine has an Elo grade of 3300. Has a Grandmaster ever beaten it in any game? If so which grandmaster and when?