I used to. It was fun. Now i'm trying to sell my rear wheel. Want to buy it? Surly fix/fix hub, DT Swiss spokes, Velocity rim. :) I thought it was good to learn how to spin but now I just ride my road and mtn bike.

i ride fixed everyday on my commute (soma rush w/ 46x16)

when you ride fixed you need to be proactive about staying on top of the spinning so that you spin (you don't get spun). this pushes over into my road riding in that i tend to do far less coasting, or even spinning without some pressure.

i actually enjoy the engagement of it...i need to be thinking about what i'm doing and that's just a little more fun than just coasting my way in to work

I have a fixed gear cyclocross bike I used as my winter commuter. It has the flip flop hub...freewheel on one side, fixed on the other.

My only gripe is that I find I spin less, since the terrain where I live is hilly and the gearing is not ideal for all. But when I power up a hill, it pays dividends later on.

Mine is a bianchi sanjose. Steel is real.

Yup, commuter for riding around town. In fact it's my avatar photo here.

I don't ride it much anymore because the streets where I live aren't very bike friendly, and a geared road bike is actually much more appropriate for the death race. I built mine when I was living in Monterey, CA and could cruise around town without worry.

As far as stroke mechanics -- meh. When I was riding my fixie/roadie equally I would say I learned to coast less on my road bike, which had benefits. I think I've seen articles, though, that suggest the old theory of riding a fixie in the off season to help your pedal mechanics has been shown not to be as effective as people once assumed.

I have been riding a fixed for the last two years as a commuter bike in NYC. I ride over the Brooklyn Bridge every day and there is a decent climb back up to where I live. It has seriously paid off in terms of my overall fitness and of course my cycling fitness
My commute is not long, but 5 miles 2x's a day while working a hard gear has definitely made me stronger. I'm guaranteed to ride at least 50 miles a week BEFORE actual training rides, plus when I get home I'm all warmed up for my run or bike. I am a slightly better than average age grouper. I personally can't see how it could possibly affect your skills in a negative way.

I have a fixed/freewheel hub which I've never turned around yet. I find that, along with 'tri-ac', I prefer the feeling and engagement of riding fixed... keeps me more alert and careful in congested areas. Plus it's more fun

My only advice is to make sure you are fit well to the bike as mashing that gear can take its toll on your knees if your form is a bit off.
good luck and enjoy!