Originally Posted by sivat
I don't think what the OP asked about has anything to do with skid patches. If both the chainring and cog have even or odd teeth, the skinny links of the chain will always hit the same teeth, and those teeth will wear faster. If you have an odd/even setup, the skinny links of the chain will alternate on the ring/cog and make for more even wear. You can see this if you are running both even, every other tooth on your chainring will be dirty.
Still..if you periodically remove your chain from the cog/chainring for cleaning or whatever, you don't need to worry about the number of skid patches or uneven tooth wear, since the chain will not go back on the exact same way every time. How many of us leave our rear wheel on the bike, without removing it, for the amount of time it takes for a drive train to wear out? I certainly don't. By chance, my ratio is even/odd, but if it was odd/odd or whatever, I'm quite sure that my chain gets moved around enough to circumvent either of these problems, so its just not something to be concerned about, except for maybe a few freak perfectionists.