We had Netflix in the Fall of 2004 and it was great. As the holidays approached, however, wait times increased and delivery times increased as well. Right around Christmas, when everyone was home and wanted to watch movies, we weren't getting anything! I think it was a combination of increased subscriptions for winter, gift subscriptions given for Christmas, and increased mail volume due to people sending Christmas cards and gifts.
We got Netflix again this summer for a few months. I have no idea why, but movies that Netflix was listing as "sent" were taking 3 or more days to arrive, when they had taken no more than 2 days during our prior subscription (except for the holidays). Also, during our latest subscription, we had to report 3 movies missing in 3 months -- two of the movies were missing FROM Netflix and one on the way to Netflix. All of the movies magically were recovered by Netflix in some magical fashion. Personally, I suspect that Netflix has such a large number of subscribers that movies are not being processed on the day they arrive.
If you really want to watch one of the movies that has a long wait time, delete all other movies out of your queu. It may take a couple days of waiting, but if there are no older movies in your queu, Netflix will send you one of the new movies.