Without violating too much opsec, I am the head sysadmin at a large government contractor. I deal with a lot of UNIX & GNU/Linux servers, a bunch of Windows clients, and (for some reason) a bunch of production machines (PLC controllers) have also fallen under my jurisdiction. It was fun for a few years, but in all honesty now it is getting a little bit routine and monotonous. The hours are not great, you are basically always on call, but the pay is pretty good. This is not really where I want to spend the rest of my life, and I recently created a technology related startup with a few friends where I get to do a lot of fun software development and EE stuff. I am not sure it will go anywhere, and I am not planning on quitting my day job any time soon, but it is fun and keeps me entertained.
If any of you have any questions about what it is like as a hardcore sysadmin/netadmin/securities guy, or what the startup life is like, feel free to ask.