I ran across their website about a year ago; it looks interesting.

yes. lots of fun. also check out punternet. go to the field reports, select london and for lady's name say contains "part" without the quotes. you'll get all of the parties

You pay just a flat amount once.

I recently attended a Lady Marmalade Monday MILF party (review in the works), and attended GP and some other parties a few years back, I would recommend Lady Marmalade over the others.