At some day you decide to test your new webpart and unfortunately web part bombs badly and you end up with page which looks something like this :
Now second thought is to open the page using Sharepoint designer and removing web part , but to the height of disappointment even Designer throws all kind of error.You are all stuck thinking "How can i remove web part ? "
Well trick is to append your page url with querystring " ?contents=1 ".
So if your stuck url is http://localhost then append the query string
This will take you to the saviour page "Web Part Maintenance Page" ,remove the webpart and have a happy day forward :)