VS2010. Mainly the fact that the user interface is painfully slow[1] (either that or I'm unreasonably fast which is rediculous as Vim can keep up with me) and it just dies about 5 times a day on a good day. It might be the solution size though - it's got about 0.5 million lines of C# in it. Still it should work.
[1] On a quad core Xeon with 12Gb RAM, SAS disks and ATI FirePro card.
[1] On a quad core Xeon with 12Gb RAM, SAS disks and ATI FirePro card.