Baseboards before or after skimcoating?

It's not easy to make a whole wall totally level by skim-coating it. If it pretty close and the gaps at the bottom aren't too bad, a thin layer of caulk is applied to the top of the baseboard to hide any minor imperfections. This is common practice. It is also very possible that the baseboard is a little warped. Either way, once its nailed to the wall and caulked, you probably wouldn't know the difference if you hadn't seen the project before it was finished. Good luck.