In normal circumstances an IP address will only trace you back to your service provider, some ISP's even use dynamic IP addresses which change everytime you reset your router.
You'd have to have done something wrong for your ISP to give your usage information to anyone else, but it does happen for example if the police want to trace somebody on the internet the ISP will in certain circumstances provide them with details of who was on a particular IP address at a particular time.
You can spoof your IP address using various methods but there is always a route to be found that leads back to your keyboard eventually.
Most privacy defaults to the fact that unless you are up to something really sinister nobody is particularly going to be that interested in what you get up to when there are several billion others out there that nobody takes any notice of either.
If I think or get a feeling that anything I might do on-line is going to come back and bite me in some way it's normally a good cue for me not to go there.