From bank sites to social media sites, it's a good idea to change the passwords to these sites at least once a year. They define your identity on a financial, technical and personal level. If you can, keep separate passwords for each of your sites. If not, at least keep different passwords for your financial and personal sites.
If you're on a Mac, you can use 1Password to track all of your passwords. To check the strength of your passwords, you can use a site like Microsoft's password strength checker or Password Meter.
Okay, enough with "the sky is falling" attitude. Now's a good time to update your personal and professional information from LinkedIn to Flickr to Facebook. With the economy the way it is, it's good to keep your public ID as updated as possible. Update your skills, update your goals, reach out and network. New people will need to know who you are now, not who you were a year ago.
Delete Unneeded Cookies
WARNING: Geek Content Go into your preferred browser and clear those cookies you don't need. Personally, I clear all of my cookies. That way I start from zero and rebuild a useful cookie library.
Organize Your Bookmarks
Just as you do with the cookies, go into your preferred browser and clear those bookmarks you haven't had a use for in months. At the very least organize them into folders.
Remove your link to those Facebook connections you really don't pay much attention to. It will help reduce the information overload. Like Clay Shirky said, "It's not information overload. It's filter failure."
Remove Unnecessary Email Alerts
Transit delay email alerts are the bane of my inbox existence. They were supposed to useful, but ended up cluttering my email even more. So I stopped them. If you have the same kind of problem, execute the same solution.
Look for better aggregators
Look for one-stop-shopping tools that bring multiple online accounts together. If you have multiple chat accounts, consider using Beebo. If you have multiple Twitter accounts, HootSuite.
There's a great article on managing multiple profiles over at Mashable.com.