I found I spent alot of time, zooming in and out of web pages to get high resolution screenshots for documentation for the apps and websites I made, so I made a Chrome Extension that makes is super simple. Just launch the extension on any website, choose from either 5 times zoom, 10 times zoom or a fixed width or height and then just drag a box around what you want to capture and you'll then get a super high dpi screenshot.

Let me know if you find it useful or have any questions. Also, please let me know if you find any sites where the screenshots aren't right, some sites do funny things with CSS which throws the extension off.