I'm on a few groups and mention or quote WikiTree as often as I can ;)
One other thing I have done with Ancestry - my own trees are very private but as I'm doing a One Name Study - have started to use a small icon, as I upload it to the gallery and put the title in I copy paste the profile I've just uploaded so it comes up in search results as public and the first thing they read is WikiTree and the profile name. I've since been contacted by quite a few members through Ancestry and WikiTree at the moment they are still wondering and deciding either way, it is one way of promoting the website :)