I ride fixed, SS, and geared bikes interchangably and usually ride a little of each every week. Its getting the the point where it doesn't even make a difference to me anymore. Riding is riding and all three drivetrains come naturally to me. Fixed made me a stronger rider at first, but the improvements came from just riding more, and not so much to do specifically with riding fixed. However, riding fixed on techy singletrack...thats just a completely different thing altogether. It requires skill, but not the kind of skill that will help you with other kinds of riding.