The large majority of people skip over them. As BoomBoom said, the law doesn’t even expect people to read all the fine print. There are many legal cases where the judge holds it against a company that it buried something important in the fine print (sometimes calling on companies to put important stuff in large font and bolded), based on the assumption that very few consumers read terms and conditions documents.
On a moral level, it is of no concern if you don’t read them. On a legal level, I’d suggest it for very important things (like an employment contract), but not for things as simple as website usage.
As evidence that even companies don’t expect you to read them, some companies use it as an opportunity to push unwanted products called foistware onto your PC (such as Java bundling garbage browser toolbars) by sneaking in an “I agree to install [application x]” part with the terms and conditions because they know we hit ‘Yes’ without reading the fine print. (For more on that, see A close look at how Oracle installs deceptive software with Java updates).