My campaign (started back when 4e came out just over a year ago) has had 23 game sessions. These last 5 hours on average.
The players were level 9 by session 21.
This was too slow for us. So, I ran an "individual" game, one for each player in one month. Basically we hit a point in the story where the players needed to split up to accomplish individual tasks that would help them accomplish something bigger when they got back together. So, for example, one game followed the Fighter and the other players played new (quickly made) characters that were helping him with the understanding that during this time their primary characters were off doing their part. Next week, we played a game for the next player, etc etc.
At the end of each of these, the players leveled their character to 12 to a) bump them into paragon which we wanted to hurry up and get to and b) to simulate how important these individual tasks were and how much time had passed when they finally got back together.