Never. I've been using Above.com for about 3 or so years now. It takes a lot of the drudgery of testing one parking company after another, resetting the nameservers, tabulating the results of each test, changing the nameservers again to the winner in the tests. that's about 4 companies x 2 months = 8-10 months of continual work (of course depending on how many domains you have). If something changes from the status quo, you need to pick up those changes (after you are satisfied that it really is a change, another 2 months of tabulating and checking), and change the nameservers to the new parking company. Above does all this for you, in real-time. without you having to do anything. It's a godsend. Of course, I'm assuming your domains are getting type-in traffic, not bots. You might also still need to tweak your settings for each domain at each parking company. But since Google mostly decides to use their keywords, not yours, the most important factor is already taken care of.