I actually spent the day working on adding Stripe integration to a Django application for my startup. Since there seem to be a number of Stripe people on this thread, I thought I might give some feedback.
It was fairly straightforward to add a custom credit card form, but not as easy as I had expected. You've made a really nice form with Checkout, but that isn't flexible enough for many users. You leave a fair bit of work to your customers if they use the raw Stripe.js library. You mention your open source jquery library for doing client side validation [1], but don't provide any good examples. In particular, the neat trick in Checkout where you show the logo of the type of credit card being used isn't documented anywhere. This blog post [2] is a crucial piece of information. Your Django examples seems a little out of date, as you've been using Flask for your python examples.
In short, I spent a day pulling things together, and got a form that has many of the nice features of Checkout. That's cool. However, you should really make it dead simple for your customers, with good examples that give ultra-slick validation and results.
Thanks for listening, and continue being great.