I run an internet book group/forum and am a member of many more. For some reason this appeals to me more than actual real life book groups - possibly because I enjoy having the time to think about the posts made by others and what they are saying. Having it on the interent also means you can always turn up and if something unexpected pops up one night, you can easily contribute the next day because it is not time specific.
During the summer I did, however, go the The British Library for discussions they were having as part of The Big Read, a BBC production to find the Nations Favourite book. This was most interesting and is just a pity it ended after 10 weeks.
For those who mentioned bookcrossing.com above, I 'released' my first book last week. It disappeared from the place I left it but no-one has written a journal entry. The book was David Copperfield though, so it may take them a while to read it
Mxx