I'm advocating the use of cmake principally for one reason -- the capability to generate project/solution files for a variety of platforms and ide's (such as Eclipse, Visual Studio, mingw, make, etc.).
At the moment I'm looking at using omnet in conjunction with osgEarth to visualize a simulation. osgEarth and OpenSceneGraph both use cmake as their build tool - an increasing number of software projects are using cmake. I personally maintain the openeaagles framework, and quite frankly I'll will move in that direction soon.
Bottom line is, if omnet leveraged the cmake system, it would be easier to create Visual Studio compatible libraries to link to other projects and more generally, its 'build' system would be more inline with something that is becoming more 'standard' - if there is such a thing.
Doug