A couple of patent law professors run a great patent law blog called Patently-O, and they recently came up with a great chart showing how long it takes to get a patent issued once it's been filed — an average of 34 months. If you're interested in patents, you should check out Patently-O — it's got great commentary on most of the important patent cases from the last several years.
You can also check out the USPTO's Patent Dashboard, which I reported on a couple of years ago here. It has lots of information, updated monthly, on pendency statistics for patent applications. An excerpt appears below: