Last I checked you have to pay for similar web if you want any quantity of data, I think they give you like 3 checks for free daily per ip, might be a bit more then that.
I am thinking of purchasing this Metrics Checker plugin, it looks interesting for analyzing the competition.
Kind of an old thread you drummed up here. Personally I don't use it a lot because Im working on building some stuff that does not require metrics at this time. I have used it though, and it was rebuilt since the last I posted about it so it is better then ever and has more metrics then ever.