Windows has long had a reputation for slowing down with time, and many people believe it needs to reinstalled periodically on a clean disk to restore it to efficient operation. I had never done that with my Mac. My current Mac is from 2010, and it has gotten painfully slow. I am someone who tries out lots of software. I went through and removed a bunch of programs that I no longer use, but the machine was still too slow to use.
Tonight, I cloned my hard disk, erased it, and reinstalled Mac OS X Mountain Lion. It feels quite a bit peppier. I have started to reinstall software. So far, I have reinstalled Google Chrome, AirMail, Carbon Copy Cloner, Sublime Text, Evernote, Skitch, and Pixelmator.
I previously had Firefox and Thunderbird installed. I am holding off on them for now. I would like to keep this computer running effectively for a least another year. A MacBook Pro is more expensive than many Windows machines, but it has very good hardware that can last several years. I would like to get my money's worth out of it.