I don't really know what kind of answer you're looking for but heres what I know...
They started at Luton back in 1995 with two 737-200s leased from GB
Airways. Luton was their first base. A few years later they got some used 737-300s and by 1999 they had their first factory-new 737-300s. They got 30 737-700s in the period 2000-2004 and ordered 120 A319-100s, the first of which was delivered in late 2003 (?). Since then they have ordered more A319s and the 737-700s should be gone by 2011 (?).
Just over half the 30-strong 737-700 fleet is based at Luton, I think its around 19 of them and the others are based at 1 other UK base but correct me if I'm wrong.
They serve the following cities from Luton:
Istanbul (Sabiha Gokcen)
Paris (Charles De Gaulle)
Hope this gives you some insight into U2
at Luton although I'm sure some others will kindly add to the info I've given!