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
I switched from NANT to MSBuild. The project is running in .Net 4.0.
My experience in Nant was good. The project kind of died. And when .Net 4.0 came along, it was time to re evaluate the build process.
Since Nant was last released MSBuild has come along ways. At this point, MSBuild is the way to go. It's easy to use, has many extensions. I rewrote my Nant scripts in a day and a half. The MSBuild script is 1/3 the size of the Nant scripts.
Much of the work in the Nant script was setting up the different environments. In MsBuild/.Net 4.0 it's built-in.