Blair didn't like her father's boyfriend until she got to know him just like back in episode 4 where she didn't like Dan until she realized what a great guy he is.I believe Blair's problem is that she doesn't want things to change between the people she cares about because she didn't want to be seperated from her best friend and she didn't want her dad to care about her any less.But the best part of the episode is when Dan & Serena finally went all the way.Way to go,Dan!;)