IF you don't reuse them then you don't have to...
Big if there, and with so many websites around most people use one or two (hopefully) strong passwords on a number of sites. If any of them are compromised and the hashes decrypted (Lets face it brute forcing passwords ALWAYS works by definition) you now have a username, email address and password (as well as other personally identifiable information) that you can use to compromise other accounts.
Random usernames, and passwords on all accounts for every web site you access are well beyond most mere mortals, but there are a number of devices and software solutions out there to do this, people just need to invest in something that works for them and start randomizing their passwords. Personally I like MyLOK from ii2p (www.mylok.com) but it's currently only available in the US due to export limitations on the technology. Just find what works for you and use it!