I remember myself keeping large signature with lots of details about myself including my room number etc, Now I don't have any default signature. IIRC the realization came when I saw one of my mail in some HTML mail archive. It had details of my address etc.
Everyone becomes aware of how useless such signature of our are, over time, but by that time probably mails sent by you to public mailing list have made it to google's memory and a appropriate search query might give details about you which you wouldn't like to give to ppl.
I have seen one of my friend with a signature which give his email id in around 5 sites, his room number, his phone number, mobile number, etc etc. many other ppl do it to varying extent, ppl should realize how senseless these things are to the reciever of the email. Even if you don't care about your own privacy information, do care about spams, unsolicits calls on your cell, unsolicit messages on your phone(they are going to be a big problem as programmes searching for email addresses starts understanding mobile number too and map the number to the email address for the person).