FYI and FWIW, in my social and work circle (large software firm in the Seattle area), people say "FYI" out loud (as well as writing it) all the time. It's as often as not in the form "Hey, just FYI, I'll be OOF tomorrow". They pronounce "OOF" as well (out of facility, meaning out of the office).
"Off the hook" in this sense means "very good/impressive/wild". "(to be let) off the hook" can also mean a reprieve, but that's not the sense being used here.