Mono developers have been working on various long-term projects to address Mono's performance after for years believing in being correct and slow rather than wrong and fast. There's been initiatives like a Mono LLVM back-end and Mono.SIMD for speeding up Mono, but now they are building their own performance team to take on these challenges.
Mono developers want to treat performance improvements as a feature and more closely monitor performance changes in their software. They've begun adding performance counters to Mono and are working on other software to help them fine-tune the performance while still hiring additional developers.
More information can be found via Miguel's blog.