While Dropbox public links are very useful for sharing files with your friends, a lot of files (text files, MP3s, PDFs, and others) will automatically open up in their browser. Here's how to get them to download to their hard drive instead.
Reader the-soup explains a simple URL trick to tell Dropbox to download a file:
If you want a Dropbox public link to download instead of show in your browser, add ?dl=1 to the end of the link. This only works for files in your public folder, with the links like http://dl.dropbox.com/u/*******/ketchup.png and not for the ones that are like https://www.dropbox.com/s/****************/Natan.ttf.
It's a simple tip, but it's actually pretty useful if you're trying to share files with your less tech-savvy friends. I know if I shared, say, an MP3 file to them via Dropbox, they wouldn't know how to save it to their computer from their browser's built-in music player. By adding this link, you save yourself the trouble of explaining how to get that file into, say, iTunes from that browser window.