Are there any major drawbacks to using a track frame as a frame for a fixed-gear or single-speed commuter? I follow a few communities which have a lot of fixie and single-speed riders. Most of the riding discussed is commuting around the city, and often, riders will show off their new bikes, upgraded hardware, or will post photos of parts needing maintenance, seeking repair advice.

I've noticed that many of the bikes are in fact track bikes, based on the track fork-ends where one would normally find dropouts.

Does using a track frame for day-to-day city commuting have any drawbacks, either for the rider, or for the frame itself?
Real track bikes don't have brakes. You need brakes for commuting, especially in a city, and at least 2 independent braking systems. Not all frames and forks have brake mounts. You also won't have fender or rack mounts which are nice in wet weather. 

Ergonomics and geometry can be an issue, given that track bikes tend to be a bit twitchy and aggressively positioned.

A lot of people use them in an urban environment, probably because of fashion and some sort of bike messenger fantasy.