I'm about 6'3" and 250lbs and started commuting a couple of weeks ago. I started on an old mountain bike I had in the garage that had one of those padded seats on it. My butt (and other close areas) would go numb as would my hands on my 6 mile commute. After a few rides I bought an entry-level road bike that came with the smaller seat with every intention of switching the seat out. But after I adjusted to the seat I have no need to change to a cushy one and have no numbness. It was after that that I read in these forums that the cushy seats can actually cut off circulation and cause numbness.

For me, just a matter of having a better seat as well as trying to get the bike seat/bars adjusted as best I could (using info I could find here and youtube) made all the difference for me. I'm still overcoming the burn, and there are still some adjustments to make but my ride is much more enjoyable now.