Like people have said, probably depends on who is saying it, I say it to people when we leave at the same time from work just as I would say, drive safe, safe travels, get home safe etc.

That said I think that it is warranted to say similar things to some people not in such a nice way as I see a lot of people doing unsafe things around Chicago. Especially going the wrong way on narrow one way streets, many of which have no or few street lights, and many cyclists don't have bike lights. It makes me uneasy when this happens even when I am on my bike as 2 bikes (one on each side) one going with traffic, the other against, and a car in the middle...not a good position for anyone.

So I am for encouraging good behavior, for everyone.