if posting random things nobody cares
if posting sensitive stuff use TOR browser, scrambles ip addreses, distributes, multiple loops, etc, fully safe
if you do it from starbucks you are golden
read the privacy policy here, all they collect is already posted on the site with the exception of the posters ip address
they disclose ip if you post a threat to people or property or if they get a court order
getting a court order is very hard, the plaintiff needs to demonstrate a legal case, given the 2nd amendment, 99.9999 of stuff here would not pass the legal muster, that is why facebook and twitter are still up and why you see people calling obama a terrorist and murderer all over the web.
just make sure you do not threaten anybody, dont name names, you are good then