Many times, and sometimes managed to make it happen, but with mixed results. Karlie Simon at LMP is good fun, but you shouldn't expect a full on PSE like in her vids. Pretty much the same for all the pornstars you can see at parties (past and present). Back in the day had fun with Majella Sheperd/Angelina Croft, Angie George and saw Tiff Walker a couple of times, and once ended up spending a small fortune (at the time) to have a disappointing punt with Vicca (environment / set up rather than her attitude or looks). More recently have seen Rio Lee, Valerie Fox, and a few at LMP such as Delta White, Delilah Dash and Karlie Simon (plus a few others).
Makes my want to write a list now. Oh and I'm hoping to see Jill Kelly when she's over in October.