We borrowed heavily from the 37signals signup page design. But the code, styling, and images were created in-house. That is, we didn't just do a copy-paste. We minutely analysed the design, recreated what worked, discarded what didn't. For a broad illustration of this point take a look how their site falls apart in IE9:
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But the 37signals signup page design is hardly divine inspiration. Go to any gas station and see the exact same design:
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As you can see 37signals borrowed heavily from the designer Joe Shmo at Texaco. In short, no design lives in a hermetically sealed box. Everyone gets inspiration from everywhere.
Or, as Pablo Picasso once said:
Bad artists copy. Great artists steal.
Thanks for asking! (P.S. you don't have to be anonymous to question our decisions.)