I ran into this problem, and wanted to leave what I experienced here in case it's helpful for anyone else musing through the interwebs for this.

I am using Homestead as my development Environment on a Mac. I am also making use of Laravel's new Elixir.

Node already comes installed on Homestead (yet another 'Yay!' for Homestead). The node-module, laravel-elixir, depends on gulp-sass. In turn, gulp-sass depends on node-sass. Node-sass, when installed, runs a postinstall script that detects your system OS and does something (I'm not really sure what).

So, if you were to create a new laravel project, and run "npm install" in your homestead (Ubuntu) environment, after node-sass is installed, it will detect a linux-x64 and (seemingly) do something that's specific to a linux-x64 environment. If you run "gulp", or "gulp watch", from within Homestead you'll be pleased that gulp runs just fine, but the VM can't send messages up to your Host computer, and you might see 'notify-send' not found, or something. This may cause you to think you can just run "gulp", or "gulp watch", directly on your Host computer, but if, like me, your Host computer is not a linux, you'll probably get a

'sass' errored after 8.19 ms
Error: `libsass` bindings not found. Try reinstalling `node-sass`

Just run "npm rebuild node-sass" from within your Host computer. IIIFFF you have node installed on your computer, it will rebuild node-sass, detect whatever environment your Host computer is, and (seemingly) do something specific to THAT node-sass build. Run "gulp", or "gulp watch", from within your Host computer. Boom. Growl Messages.