So this is my first attempt at multi-boxing. I did some research and decided on GCP as a platform. Here is an overview of the first night.

Purchasing process-
Very easy, received key instantly after entering CC in a secure paypal form.

Installation-
Quick download, easy install. I did not see anything about installing the GCP WoW addon, so I did a quick search of the forums for addon and found a link and popped it in my WoW directory. This might have saved me some trouble, not sure, the program might do this automatically. The program does not verify you have .net framework 3.5, so make sure to download it first, or you will get saving errors!

Setup-
The Wiki is very informative and the step by step videos are a huge bonus. I read over the wiki first, then cracked open the program and followed along with the video tutorials was up and running quicker then I expected and most of my time was spent tinkering with the layout and custom video settings for my main window.

Using the program-
It works! It is intuitive in many areas. I have a lot of questions and stayed in the simpler mode but I was multi-boxing (on one box) in one night. Unfortunately it takes up to 72 hours for new characters to party while they verify your credit card now, so I was partying without being in a party. Good practice using the program to control each character from my main screen though.

Overall-
Very impressed. Up and running in about 2 hours including setting up 3 new WoW accounts, repositioning my monitor configuration, tinkering with game settings, wondering why Blizz wouldn't accept my CC (had to remote into work and pay from another IP address), trying to party my characters every 5 minutes just to see if it would work, etc. Sweet application and developed in Visual Studio 2010 I assume, very up to date. I would recommend to anyone who is thinking about multi-boxing, if a little bit of complexity involved in using the program scares you, perhaps you should not be thinking about managing a multi character team.