COM is horrible to write code for (although not THAT bad), and is tricky to troubleshoot (hurray for TLBs and massive hex registry strings) but it is a very handy feature of the system!
Does anything exist on other platforms like Mac OSX and Linux? CORBA was written all over the place GNOME1 / 2 time as I recall but I don't actually know if anything like COM exists anywhere?
Gecko uses XPCOM extensively (though less than it used to). XPCOM is basically a cross-platform implementation of the same principles as Microsoft COM.
In particular, XPCOM allows easy binding with the Spidermonkey JS runtime so you can expose things to scripts.
COM is not only proprietary but also a horrible thing. I don't see it ever being on any Linux list of things to do.
It will never install on Linux.
If you want something as good as Visual Studio on Linux, write it.