So on the my friends feature can we mix people from all countries and we can be in more than one group, right?  Is there a limit to how many groups we can be part of? 

Yes - you will be able to either have an online or physical group (or both) - if it is physical then it's still up to you as the Group Owner who you allow in and under what reasons you deny them (location might be one of them).

I am actually working on the new version right now and I am basing it on YouTube's Groups implementation, but better ;)

Thats a nice thought actually - if it is an online group to be able to see when your friends are online and which poker room they are in! I'll have to think about that...

Please note that the new version of Groups has now been released and you can specify the Country (if required). You can try and create a group here.