It's anywhere from 25%-35%. Weekend Update is always pretty good, but most of the skits they air are either A) not funny or B) retreads.....meaning it's the 943rd time they're showing "What Up With That?" or "Scared Straight." Those retreads kind of lose their luster after you've seen them many times.
I saw every episode this year, and would estimate that, in most episodes (exclude the January Jones and Megan Fox episodes), 1 out of every 3 or 4 skits made me laugh.
They should dump some of the recurring skits like "The Kissing Family." I want to see more of Steve Harvey hosting something or Keith Morrison ("Dateline NBC") giving his creepily happy analysis of an event.