oh the poke button is just like poking someone in real life, it doesn't invite them to your house, it doesn't say hi, and it doesn't mean your interested, it simply means, im going to poke you, and you can choose whther or not you want to poke me back. you may be thinking 'well thats pointless' but well, thats just the charm of facebook. it was developed by a kid, what more can you expect.
no its not ok, some people add other people that they don't really know, such as an acquaintance, but i don't think people randomly accept friend invites from others, unless they want to say they have more friends than they actually have. but be safe, don't add anyone unless they're at least your acquaintance.