The tc command with the netem kernel component provides a means of emulating your network connection in order to test how a site might perfrom for users with limited or saturated network access. This can be very useful in determining minimum requirements for the best user experience as well as in optimizing performance and improving the experience.
There is a great gist (slow) that combines them well to make it easier to change settings on the fly with presets. The git is written in bash and can be updated to add more presets (please consider forking in gist and sharing your enhancements?). Check these out if you're looking for more detail via Traffic Control HOWTO and netem