I don't think that a commuter bike is that much about compromises, it's a bike with a purpose. When you commute some things are not all that important, top speed is one of them IMHO, weight is another. Of course, this depends on what your commute is like: urban, open road, trails.

So for me, an urban commuter, a mountain bike with heavy wheels and thick tires is not a compromise because I probably won't even want to go faster than 15mph on crowded streets anyway (I can maintain 20mph comfortably though). It fits the bill perfectly because what's more important for me is toughness, comfort, all-weather ability, ability to carry cargo in waterproof bags and stopping power.

The bike I ride right now, that I just built in December, is as close to my perfect commuter as it can be. It satisfies my needs without any compromises. I commuted on several different bikes over the last few years including a regular road bike, a singlespeed road bike, a hardtail MTB, a full suspension MTB and each had some advantages and disadvantages but the road bikes were the worst for my commute. So that's why I decided to build my own commuter based on all those experiences. I tweaked it over few weeks and I shaped it up to be a nearly perfect commuter. I'll just get new wheels and upgrade from old Hayes brakes to Avid BB7 and it will be done!

I will be able to commute on this bike any day, during any season, during any weather, I'll be able to bring with me anything I may need for my work day, I will be able to run any errands I may need. I just have a another wheelset with studded tires for quick swap. So for me this is a do-all commuter.

Now, can you have one bike that will DO ALL, including everything else besides commuting: trail rides, club rides, organized events, heavy hauling, touring. My guess is: not really

Adam