|I’d suggest you visit http://go-mono.com. They have lots of information regarding .NET there, and go into details regarding why it’s good to have on Linux.
In short, the advantage is that it’s a complete Open architecture for application development. If offers all the features of Java (security model, JIT, etc.), but is more open, and (in some ways) much faster and more flexible.
Some people say that Mono gives MS control of Linux. not even close. MS has *no* control over Mono. And, even is MS changes their standard and makes MS .NET incompatible with Mono .NET, Mono can still be used – we just lose the interoperability, which would be the exact same thing as if we didn’t have Mono at all.
In short, tho, the real reason behind Mono is: it can’t hurt, and assuming MS plays nice for once, it’ll make Linux desktops much more interoperable with MS C#/.NET applications and services.
It should also be noted that Mono is only the .NET Framework. MS .NET is the Framework, plus a bunch of extra utilities and add-ons, plus a whole range of web services (thus your 20MB download). Mono is not any of those thing.