I don't trust software or web solutions to manage files for me in a consistent manner over the long length of time I want to keep things. Software dies, web sites die, but directories are always there.

I use a browser plugin to capture the complete page, then I save it to a DropBox directory with the URL and timestamp included in the file name. The plugin I currently use is "Awesome Screenshot" for Chrome: http://awesomescreenshot.com/