I've done grouptherapy twice (actually three times, but the last time I quit after two sessions). The second time was for a year and there were so so many times I didn't said anything the entire session. But that was also my problem (social anxiety). Group therapy isn't really something for me.
There have been sessions when another member didn't said anything for the entire session. Sometimes another member would ask that person about it. Group T's aren't always the best T's, in my experience.