I was using Windows 7 for a time and couldn't live with how slow the OS was getting. Simple tasks were starting to take an eternity. Running them on a multi-core Intel CPU, with 4GB RAM, and it started feeling like a 486 running XP. Windows bloat is gonna get ya.
I installed Debian Testing this morning using Net Install. It is fast by comparison. Running on the same hardware, there's little to bog it down. Linux has a small footprint, and Debian is lean and mean.
I start with a minimal install and add the stuff I need as I go. Just the essentials: Chrome Browser. Emacs. MPlayer. And a couple of other goodies thrown into the mix.
Now the machine feels lean, fit, fast once more.