I currently use nant, ccnet (cruise control), svn, mbunit. I use msbuild to do my sln build just because it was simpler to shell out.
Are there any merits to switch
We also switched from nant to msbuild. If Your build is pretty standard, then You won't have much problems setting it up, but if You have a lot of specific build tasks, You will have to write custom ms build tasks, as there are way less custom tasks for msbuild.
If you want to display reasonable build results, You will have to mess with custom loggers etc. The whole team build is not as ripe as nant is.
But the real benefit is integration with TFS source control and reporting services. If You are not using TFS as Your source control system, it's not worth it.