LinkedIn recently was hacked and had its passwords compromised. I highly suggest using separate passwords for online accounts. Use one set of passwords for banking and other important sites and different password for Facebook, twitter and LinkedIn.
The reason for this if a password is compromised; they do not have access to all of your accounts.
To make things really secure, I would recommend using a password vault product live password safe. It will keep your passwords in a database that is encrypted; you just need to be sure your master password is secure.
Embrace the use of separate passwords.