I think I've just about given up on the apostrophe in "let's" -- it seems to be dying out rapidly (replaced by the sleeker "lets"), and I'm tired of fighting for it.
I am, however, holding on to "fewer." It's been over a year since I've heard anyone other than myself use it, as "less" expands beyond its neighbouring kingdom to take over the lingual territory formerly claimed by "fewer." (eg. "I have less jelly beans than you." "I realized recently there are less days ahead than behind.")