[jarofgreen]

As well as what the others have said, various bits of software make the assumption that 1) may be private and to be careful with it and 2) isn't.

eg Your web browser will automatically save any URLs to it's history for any user of the computer to see but will ask first before saving passwords.

eg Any web proxies your traffic goes through or other software that's looking like virus scanners will probably log URLs but probably won't log form contents (yes HTTPS makes this one more complicated but still).