Although I haven't been around as long as some, the "oops, wrong side" posts seem to have greatly decreased after the update where the home page now has latest posts separated by BG and DB. There tended to be a lot more "I just clicked on this, skimmed the first post and commented" when they were mixed together, and some topics were particularly vulnerable.
I am guessing that there are still people who contribute on both, open multiple threads/tabs and get confused, and/or autopilot internet. I agree with Chris that statistically it is more likely to happen one way than the other.
