Haha, no, it's perfectly legal. Almost every site and service will keep activity logs with IP addresses. There's even been talk of making those logs legally required for law enforcement purposes. Your ISP already most likely holds logs of everything you've done online in the last six months too.
However, contrary to popular belief an IP address is pretty useless on its own. To find out who was behind the IP address you have to get the ISP to tell you who had that address at a given time. To further complicate things, multiple people can have the same IP address on a given day. Indeed, if you look at court briefings of people busted by the FBI for internet crimes you'll find that often multiple other, innocent people were raided because they shared the same IP address during the times the FBI was interested in.
If you're concerned about being tracked you should be more worried about cookies and scripts. In addition, your browser can uniquely identify you everywhere if its header is unique enough (if you use firefox with a ton of add-ons, for example, you may very well be the only person in the world with that browser fingerprint) since sites also see browser headers.
None of this is usable by an adcom or other forum users though. If you're worried about that all you need to be concerned about is the stuff you say on here.
