Odds are you've given lots of applications access to the services you commonly use. Maybe you've used more than one Twitter client, a Facebook app or two (or 20), or an Instagram plug-in of some sort. Over time, we tend to let an enormous number of things attach themselves to our accounts, with varying degrees of permission. It's a good idea to go through periodically and clean these out.
Like, today. Right now.
Google, Twitter, Facebook, Dropbox and lots of other services support OAuth, which enables third-party apps to use account APIs without having to give them the actual account login information. Seems harmless, but it also could offer a malicious application or individual access to your account. If you're no longer using these services (or even only using them rarely) there's little reason to allow an app to continue to have access. Here are the links where you can go to clear off the cruft:
Google
Facebook
Twitter
Instagram
Dropbox
There are probably quite a few things on each of those lists that you completely forgot existed (Gravitar? Plaxo? Cliqset?). Go ahead and zap those. Also, anything you haven't used in more than a month or two should have its access revoked. You can always grant a service access again later. That's certainly much safer than leaving an authorized connection just dangling there, unused.
While you're at it, clean up the list of authorized services within your mobile applications. Try this: Go into the Twitter app's settings on your phone and check out how many third-party apps and services you've authorized Twitter to share data with. Yow! Now envision how many of those you can live without.
