True, a lot of the heavy lifting is done within the runtime. However Mono has been improving at a break-neck pace over the past few years - Mono 3.x with the ne

True, a lot of the heavy lifting is done within the runtime. However Mono has been improving at a break-neck pace over the past few years - Mono 3.x with the new garbage-collector and LLVM backend can be quite efficient. Furthermore F# is bundled with Mono nowadays so hopefully they are aware of/fixing any issues with functional-style code, e.g. tail-calls. I used Mono and F# for a project earlier this year and had no particular performance or behaviour issues, although my work was not generally performance-sensitive.