Upgrading Snow Leopard to Mountain Lion and preserving Bootcamp partition
I have succesfully upgrade two machines without having any issues with the Bootcamp Partitions or the actual installation. The upgrade doesn't seem to the touch the actual partition scheme unless it is a HFS partition. I also did the upgrade on a Tripple Boot MacBook without any issues.

I have also done a clean installation of Lion onto a machine that had a bootcamp partition without issues, as long as you don't delete the partitions.

As always, make sure you have a backup of the important Windows portions as for safety, however go ahead with the upgrade, it should only affect your existing OSX partition.