gtg frequency question

hello. i did a couple searches, but to no avail. are tb gtgs a once yearly thing, or is it just random? as in, i noticed the sf bay area one was in february. does this mean itll next be in february 2010? sorry if this is a stupid question, but i saw the nyc pics thread, and i almost went to this years bay area one, and am now wishing i went. anywho, thanks in advance for the info.