> solve small problems for which Python/Ruby would have traditionally been used, good file system, stream and networking APIs, but concurrency as a first class citizen, garbage collected, fast startup time
I think for the most part, you won't be missing a lot in Haskell. If you are looking for what you say above, Go should satisfy your needs greatly. Haskell is amazing for functional programming needs - fast prototyping and great at doing mathematical calculations. It helps you think in another way, but I certainly wouldn't use it for building something like an API or networking.
While it's kind of off-topic, let me still ask: what are the problems you see in using Haskell for networking? I see that building a library with the C calling convention might be hard, but a web service must be pretty language-agnostic.
I think for the most part, you won't be missing a lot in Haskell. If you are looking for what you say above, Go should satisfy your needs greatly. Haskell is amazing for functional programming needs - fast prototyping and great at doing mathematical calculations. It helps you think in another way, but I certainly wouldn't use it for building something like an API or networking.