In 2010 I got a close to end of market Motorola Droid. The Droid 2 (and Droid X) were on the way.

About 4 months ago, it became completely unusable. I believe it was a new OS update combined with some of the apps I used (FB and Twitter, mainly) becoming more chatty. Facebook's app is now grabbing GPS coords on every use. I could barely make calls, send texts, read email, take photos, the core functionality of my smartphone was gone. 

So, I went through a process to flash my Droid back to its original version, making it like the day I got it. It works like a charm now.

Moral of the story:  

Don't update your smartphone's OS unless you want to replace it in less than 24 months. Cut down on the apps and use the browser based versions.