Beyond the 249 icons, my favorite thing about Font Awesome is how designer friendly it is. Just install FontAwesome.otf and visit the copy and paste page when designing. You can also contribute your own icons. Although to submit your icon, you’ll need to email Dave at email@example.com so he can approve your icon for submission vs sending a pull request. He’s keeping a very tight reign on quality.
Font Awesome’s licensing is a combination of the SIL open font license, MIT license for code, and the CC 3.0 license - making it completely free for commercial use. Attribution is no longer required for Font Awesome 3.0, but it is much appreciated.
UPDATE: Use icnfnt (The official subsetting tool of Font Awesome) to create a custom Font Awesome icon-font kit with only the icons you want. It even includes the CSS, Sass, SCSS, & LESS files. While you’re at it, check out the source for icnfnt as well.