Hmm, I too use eggs on my fixie but have never really thought of them as a security device. I think of my fenders as more a theft deterrent at this time of year than anything else. Fenders = less sporty to most lower levels of humanity.

I tend to just jump on it with flip flops if I need to make a quick run down to the grocery. Its definitely rideable, just rather hard to keep on the pedals under good power.

I think the fixed gear is the larger of the security features. That and the typically older frame, road bike components, lack of many parts, and typical less than flashy fixie style (not always the case, I know).

-Pete