dolface - smaller wheels get better acceleration if that's what you're asking.

ken cox - 26" wheels are what are on mountain bikes, have a 559mm bead seat diameter (bead of the tire), 700c wheels have a 622mm bead seat diameter, as do 29" wheels. 29" is the same as 700c but a wider rim for offroading, more of a marketing term.
I'm guessing that by 28" the original poster is referring to wheels with a 622mm bead seat diameter, a common size. Plus, apparently 622mm has also been called "28 x 1 5/8"

for more info go here http://sheldonbrown.com/tire-sizing.html