No, it is not difficult to get tickets. It just takes a lot of planning ahead, and a little luck. CoSport is the official ticket seller for the US. Way back in April of 2007, we chose the events we would like to see and submitted the info to CoSport. This was actually the second phase of requesting tickets. We missed phase one.
Several months later, CoSport emailed me to let me know what tickets we got. While we only got 40% of the tickets we requested, we were still happy to get them at all. (Things we didn't get: swimming, diving, and the illustrious Opening Ceremony.)
And no, the tickets weren't expensive either. Some were less than $10.