That's why most of everything you use runs linux. Your router, most phones, and lets not forget most* of the internet. The games you play online connect to those linux servers, and lets not forget our favorite search engine, Google.
There are a lot of instances where Ubuntu will outperform Windows 7. It boots way faster, and has loads of hardware support. Some OpenGL Windows games run faster in Wine under Ubuntu, then they do in Windows 7. Though, the same can't be said about Direct 3D, which uses a wrapper to run those games. Which puts a huge strain on the system.
Linux doesn't have the support that Windows gets with its graphics drivers. They're buggy, behind the Windows version, and behind linux innovations. Though that maybe why there's a lot of effort in getting fast Open Source drivers, which currently only do at best 1/10th the performance of ATI and Nvidia drivers.
Linux as a kernel might be solid, but your router, phones, server equipment, etc are all commercial products that are tailored for a specific purpose.
Operating systems built on linux however covers a much larger scope and are severely lacking in polish. I attend a tech school where 99% of the students have worked with Linux. While it certainly has it's uses in academia and some other fields, it's frustrating watching someone use it as their main OS. There are way too many issues if you're trying to optimize day-to-day productivity, and open source 'software alternatives' almost always fail to go head to head with their commercial (industry standard) counterparts.