We normally have at least two meetups per month. One is more study oriented and we set a topic in advance to give people time to prepare some vocabulary and phrases they can use.
The second monthly meetup is more socially oriented - so far this has been a meal but in the future we may try other activities such as going to watch a Chinese film and then talking about it afterwards.
There is a Google wave for this meetup group. Find it by searching for "with:public tag:londonmandarin" (put the text between quotes in the search box, which normally contains "in:inbox" )