The JVM is a piece of software that rivals the kernel in complexity with for the most part redundant functionality (i.e. memory management, monitoring the running program, etc.). It does have the benefit of being uniform across platforms, but if you're dealing with a single OS, then the extra weight and deployment complexity isn't worth it - you're better off learning your operating system and its tools.
Nothing, IMHO. However, I do like Go's much leaner memory footprint for server side software. At least, that's been my experience: the same code doing the same task takes up much less RAM.
Someone correct me if I'm wrong but I think not using the JVM makes deployments much simpler. At least that was one of the benefits a team at Amazon stated about switching to Go while I was there
The VM part of the JVM allows for really great monitoring: there are standard ways for tools to hook into bytecode and add instrumentation without needing the source. There are also lots of mature tools available, but that's mostly because the JVM has been around for so long.
We're looking at Go right now, and our instrumentation is currently done manually at the source level. Are there, or will there be, tools to add instrumentation similar to those available on the JVM? I'm sure it's possible...