It seems there are two different patterns how our users distribute agents among build configurations. Some of them configure this distribution with help of agent requirements and then TeamCity decides what set of agents can be used to run build configurations. Others want to specify explicitly which configurations can be built on which agents, and do not want to allow building of other configurations on these agents.
When we started developing TeamCity we decided that the first case is more common, but at the same time we allowed the second case too. However, UI for the manual configurations selections for the second case was far from ideal, and quickly starts to be very unusable with increasing number of configurations. In TeamCity 6.0 we decided to partially address this problem by providing better and more convenient user interface.
Agent requirements dialog now has autocompletion enabled. Autocompletion works for both parameter name and parameter value. The whole set of parameters on all of the connected agents is considered, and you can see how many agents have this parameters defined, and with what values.
Jetbrains dotCover is now bundled with TeamCity, and is listed as another coverage engine for .NET runners. Also HTML coverage report with detailed information is available.