I have been using it for two years (through TripIt Pro). Dan's blog post finally kicked my butt into writing a blog post about it (why I love this so much). Feel free to check it out, I think it answers most of the questions people have in this thread:
http://www.dimascorner.com/2013/regus/Also, I posted the following in response to Dan's post. Hope this helps!
I have been using this for two years now. Been to lounges in USA, Germany, Switzerland, Belgium, Ukraine, South Africa, Dubai, Thailand, Singapore, Australia, Brazil and Argentina. Essentially, it is access to office space in prime locations in big cities with decent free coffee (in most places).
The quality (of coffee, internet connection, and the 'lounge') varies greatly. In Cape Town and Buenos Aires it was downright crap. Nice place but internet connection and the computers in the lounge barely worked.
The 'lounge' itself could be anything from a table in the kitchen (with people always around you) to comfortable arm chairs in the 'lobby' to 'business pods' aka mini cubicles to a separate room with a table or two. Usually they have a single iMac available for use or you can connect to their WiFi with your device.
I have experienced issues connecting to WiFi in some lounges with my Mac products (either Macbook Air or iPhone or sometimes both would not connect).
But overall, it really is a good thing to have in my pocket as I travel around the world. Having a familiar 'face' in any big city helps a lot when you need an internet connection and have no clue where or how to get it. I am loving it!
Oh, and usually the prime location of the lounge means that you may be treated to some awesome views (without having to pay to go to a touristy observation deck).
To answer couple of the questions above - this is NOT airline lounge membership. There are a couple offices located on the airport property, but not inside the airport (I have been to one in Munich and it is located at the office building between two terminals).
Birthday-wise, I don't think it would matter. I never bring my card with me, just give them my number when I come in. Sometimes they ask for ID just to verify the name. In most cases they didn't. Note that in some countries, I had to show my passport at the office building entrance to get the visitor pass for the building in order to come up to the lounge (so make sure you carry one with you if you are outside of the US).
Oh, and my favorite pet peeve with these is how Regus is pronounced differently in different countries (and how everyone insisting on correcting me in each particular country): Reeeegus, Rehus, Reagus, Rigas and so on.