Sorry Jess! I totally didn't check the issues or pull requests at all, I just forked and went to work.
In my fork I added guard-livereload and rack-livereload as a default, and tested it on OS X and Linux. Not sure if you'd want that as a default or as a configuration option.
As far as the haml piece, I don't want to step on any toes - In my fork I added a template for it, updated the haml/sass/etc gems, and enabled haml by default in the Gemfile. I also had to monkeypatch Tilt as it ignores the default encoding of the ruby environment when loading a template, and instead forces it to 8-bit ASCII. Needless to say that doesn't play well with UTF-8 :-)
I'm super slammed at work but would be happy to change a few things for a pull request as required; especially with the live reload Serve is a tool that we can definitely use where I work.