At $50NL I never fold sets. People can go crazy with too many different hands (2 pair, TPTK, overpair, draws) for me to lay them down. Sure I get stacked by straights/flushes/over sets, but I'd need a heck of read to lay it down. Something like a solid player raising preflop, then c/r big on AT7 board (if I have TT). Though even then I don't think I could do it.