Yesterday I stumbled upon a very useful tool while (trying to) teach(ing) myself D3, namely http://bl.ocks.org. This lets you access, and preview, your webby gists in a browser - just by browsing to http://bl.ocks.org/<gist-id>. Most handy!
(The only minor down side is that there seems to be a slight latency if you update your gist before it updates on bl.ocks.org.)