They have a big fat jakob-nielsen-old-school-ugly upgrade message. We’re talking yellow-background-and-blue-links ugly. Even though I think it’s unattractive, I bet this message works well for them. I don’t know if they’ve A/B tested it, but my gut instinct is that it really works. The reason is because the message is so jarring visually. It doesn’t fit into the asthestic of the rest of the app at all.
A lot of us would rather design an upgrade message to look great and compliment our branding. However, I bet the effectiveness of “nicely designed” upgrade messages is a lot lower than this ugly-style message.