The UKBA has posted the following announcement on its website here regarding visa processing times.

In the days leading up to the closure of the former student routes on 31 March, we received many more postal applications than usual. The volume of applications, together with the fact that we are applying the same level of enhanced checks to these applications as we are to applications for the new Tier 4 category, has resulted in some delays in processing applications.

Please be reassured that cases are moving through the system and you should have a decision from the UK Border Agency in the coming days and weeks.