I've been using sloppy - requires java - to view some sites at the connection speed of slower internet users. If you're not using something like this when developing, it is a useful tool for making sure your websites load as quickly as possible even for slower users. If using FireFox, you can also download and install the firebug extension to see how quickly your page is loading at a particular connection speed.
Things that will speed up your site for such users include content compression (gzip), minimising http requests (this basically means combining image, css, and javascript files to reduce the number of requests the browser has to make per page), and compromising on fancy features over page load size - the scriptaculous pligg module is not a necessity for example. Another useful tip is to load your css files as early as possible, and (where possible) your javascript as late as possible on the page. This means that the page will be rendered before all the bulky scripts are downloaded, making the loading process appear faster to the user.
Oh and minimising calls to the database is the other big time saver.
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