Ask YC: Finding code on the internet - what about IP Rights?

What's the deal with code snippets on the internet? If the idea is to share code, shouldn't these things be clearly licensed? How long/complex does a bit of all-rights-reserved code have to be before you are breaking the law to use it in your own program, and do people do this anyways? Especially if you're coding for work, it seems like this could either be a pain or get you into a lot of trouble. What's the common practice regarding code found on newsgroups, mailing lists, fora, blogs, and snippet sites?