I'm interested to see the the trends and choices made by YC startups. Do they favour NoSQL over Relational? Are they embracing Javascript on the server? Is Ruby still the most popular choice etc etc.
Take domains from here: <a href="http://yclist.com/" rel="nofollow">http://yclist.com/</a><p>Plug them in here: <a href="https://builtwith.com/" rel="nofollow">https://builtwith.com/</a><p>You'll learn a lot from that, even though it can't peer too deeply into the backend of an arbitrary website. Lots of startups have tech blogs these days where they may have written about your stack; barring that, asking is probably the best way to get more details.