same here...but my fixie is a beast...I've got these steel araya 36H rims that are absolutely bulletproof...plus 400 gram 27x1_1/4 tires w/mr tuffys...its my urban assult vehicle. It rides nice, though, but i think that also might be a function of the ultra long wheelbase.

as to answer the original question, it doesn't matter a whole lot. however, there are not very many areas where it is perfectly level. so in an ideal circumstance, weight doesn't matter.