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 use Nant and I love it. I used MSBuild and hated it because of these:
Microsoft forces you to follow their own build procedure that is so intrinsic to their doings that I at least was not able to make it work (I had to compile NET1.1 so I had to mix Nant and MSbuild). I know you can create your own MSBuild file, but I thought it was complex to understand and maintain.
ItemTypes to do file operations are just too hard to follow. You can have Nant do the exact same things and much easier and direct (I had to create an ItemType list and then pass to the file operations).
In MsBuild you have to create your own task dll, in Nant you can do this or you can embed C# code within your script, so its much easier to advance and just build the whole project.
Nant works with Net1.1, MsBuild doesn't.
To install nant, I can even unzip and locate inside my own repository to run it. To install MsBuild is much harder since it depends on many things from Visual Studio, etc. (maybe I'm wrong here, but that seems to be the truth).
Well these are my opinions...