Note this comes from a conversation with faculty in May 2010. So if you are far from the future, this may no longer be true. If it is before 2015, feel free to contact me in some way (see my profile) and I can give you an update.
Currently Boston University High Energy theory only has two grad students who are in their third and fourth years. The BU HET faculty in the past has kept the number of students down on purpose, but they have had a change of heart (due to LHC turn on), so over the next several years they are looking for more students.
The entering class of 2009 has 4 or 5 students interested, and I don't know the final count, but the entering class of 2010 probably has 4-7 students interested in HET.
The current goal for the entering classes of 2011 and 2012 should be similar, ie around 5 interested students.
Thought I should post this good news for HET students! I think the next several years should be great years to start in HET.