> Well, what I'm really looking for is a sort
> of informal group of people about my age (I'm 28)
> that just get together and talk about writing, share
> works, go out with each other, etc.
Since I'd imagine that the sorts of people who are attracted to writing classes offered in the summer at community colleges and such would be from many various age groups, you could try contacting people you might meet in a class like that who would be your own age and try to set up a group outside of class. Or, as Christopher had written, groups like that are known to advertise in alternative papers; those you generally pick up for free around town. Just using the AltaVista search engine with the query "San Francisco" +"writing group" turned up some good results. Of course, you'd have to filter through the links yourself, as some of the writing groups listed are programming groups or businesses.