Have you been referred to a site and wanted to check something quickly but they required you to register? The answer is yes, if you are still trying to remember. It is annoying. I do not mind registering if I am going to use the service on frequent basis, buf if I just wanted to check something, I do not want to waste a minute typing up my data. I usually use a bogus email for these things anyway.
Well, worry no more, because BugMeNot is at your service. Just go there, type the site address and it will give you user names and passwords for many sites. They even have a firefox extension!!