I almost never tell people I'm lipreading them (or very badly attempting to)... I'm sure they can tell that I look at them intently. Oddly enough when I do job interviews my eye contact sucks HORRIBLY.. I have no idea why- only time is when they're asking but when I go to answer I have trouble and cannot keep eye contact...
Anyway- sometimes some do ask if I can.. I only say either "a little" or "not very well". I've never seen anyone become uncomfortable with me looking at them- that I've noticed. I still won't tell them because if I do, I'm afraid that they'll over do it. Telling them I'm deaf though seems less of a problem strangely.