What makes a good developer experience?

I want to learn more about your experience with "developer services" (tools, platforms, libraries, APIs, etc). Feel free to leave blank any sections that you don't have an answer for. Thank you for sharing!

    Basic Info

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    Your Favorites

    Here, I'd like to find out about the positive and negative experiences you've had with the developer services that you've used. A "developer service" could be a traditional Web API like Twitter search, a hosted platform like App Engine, a JS library like jQuery, or a set of tools like Google Web Toolkit.
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    Popular APIs

    According to programmableweb.com, the most popular APIs are Twitter, Google Maps, and Facebook. I'm curious if developers are using them because they have to use them or because they enjoy using them. If you haven't used these APIs, just leave the questions unanswered.
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    The End

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