IP, dosen't give them much, like your address, just gives there your location (town or city) and sometimes your service provider. An IP address is an identification of a computer and it's location. For example, if you were to search up my IP, it'll be like this:
192.168.1.121.hfx.eastlink.ca (that's just an example).
Middle Sackville, Nova Scotia, CA (Canada)
Someone website have a code, where they can collect annonymous info, such s your web browser and Operating System like this:
Mozilla/5.0 (X11; Ubuntu; Linux i686; rv:13.0) Gecko/20100101 Firefox/13.0.1
This is my user agent string, and a lot of support forums, this will be displayed in your posts. It dosen't have any personal info, basically what that means, from my user agent string is that I'm using Mozilla Firefox version 13.0.1 on Linux: Ubuntu, which is the Operating System. The i686 is the processor architecture, which I'm have a Pentium Core i3 (64 Bit), but it dosen't say that.
As you see, it's just basic annonymous info.
If you worried about someone hacking into your computer by your IP, it's possible, but not likely. Unless they hack it remotely, they would need to be at your computer. If you're using a Linux Operating System, like me, it is very secure, which means it hard for anyone to hack your computer or for a virus to get installed, becuase of constant updates, and well structured system. It's Open Source (And free of course), making it almost impossible for people to get a virus into your computer. If someone tries to get into your computer via the IP address, you would get a mesage asking that someone is trying to access your system remotely. Even if you're using Windows, I wouldn't worry about it. It's not very likely that someone would do that, never happened to me.