My perspective is similar. I do a bit of Java, C++ and Python, and recently wrote a ~1K LOC backend in Go. I figured I'd share it in case someone finds it interesting.
For low-level infrastructure projects that don't have very complicated business logic (e.g. caching systems, gateways between different RPC systems, etc.) but which run in many machines and must handle many requests per second, I'm sticking with C++. It's sometimes painful to troubleshoot race conditions around resource destruction issues, given that I use lots of async calls and threads, but still ... I don't think I'd feel comfortable investing significant efforts building this kind of systems in Go or even Java. That said, I'm trying to gradually migrate away from callbacks spaghetti and data sharing between threads towards ... specialized threads and message passing, a model far more similar to Go's. But I prefer C++ over Go and Java because it feels more predictable and, barring bugs, seems to have a lower operational cost. I don't want to imagine things like Bigtable or Google's other storage systems written in anything other than C++.
For higher-level backends with more business logic but which still must handle many requests per second, I lean towards Java. I feel that Java brings a few headaches for the production engineers that for some reason happen less in C++, such as having to tune the GC for performance and latency. Systems in C++ feel significantly more predictable, from my production perspective. But I'm willing to lose that predictability and switch to Java for the gains for the development team. I'm not sure I would be ready to switch to Go: I perceive the state of internal libraries on Go as trailing significantly behind those in Java. I guess this may change (or my perception may even be already dated).
Finally, for internal servers with little load, I'd already pick Go over Python. I come from a strong Scheme background and originally really liked Python, a very nice subset of Scheme. However, I'm coming to find projects in Python relatively hard to maintain. :-/ I feel that when Python projects hit a certain size (when a program reaches something like ~20 non-trivial classes, with some inheritance or interfaces, something like that), it becomes hard for new comers to extend it successfully. It may be just me, but I find that the lack of a canonical way to do things like interfaces means everyone has their own adhoc way to do this and ... things just get messy, or at least more messy, faster, than they do in the other 3 Google languages. It could also be the lack of type checks at compile time, I'm not sure. But I digress, all I meant to say is that I think Go may actually make things a lot better than Python in this regard, so I'm starting to use it in this area.
You'd know more about Java's strengths than I would. I haven't really touched it since we parted teams. I just remember production pain...
I'm sure the Go library situation will improve, and we can nudge that along as we write internal tools. I'll definitely start my next one in Go. I might even translate my last one to Go sometime.
My perspective is similar. I do a bit of Java, C++ and Python, and recently wrote a ~1K LOC backend in Go. I figured I'd share it in case someone finds it interesting.
For low-level infrastructure projects that don't have very complicated business logic (e.g. caching systems, gateways between different RPC systems, etc.) but which run in many machines and must handle many requests per second, I'm sticking with C++. It's sometimes painful to troubleshoot race conditions around resource destruction issues, given that I use lots of async calls and threads, but still ... I don't think I'd feel comfortable investing significant efforts building this kind of systems in Go or even Java. That said, I'm trying to gradually migrate away from callbacks spaghetti and data sharing between threads towards ... specialized threads and message passing, a model far more similar to Go's. But I prefer C++ over Go and Java because it feels more predictable and, barring bugs, seems to have a lower operational cost. I don't want to imagine things like Bigtable or Google's other storage systems written in anything other than C++.
For higher-level backends with more business logic but which still must handle many requests per second, I lean towards Java. I feel that Java brings a few headaches for the production engineers that for some reason happen less in C++, such as having to tune the GC for performance and latency. Systems in C++ feel significantly more predictable, from my production perspective. But I'm willing to lose that predictability and switch to Java for the gains for the development team. I'm not sure I would be ready to switch to Go: I perceive the state of internal libraries on Go as trailing significantly behind those in Java. I guess this may change (or my perception may even be already dated).
Finally, for internal servers with little load, I'd already pick Go over Python. I come from a strong Scheme background and originally really liked Python, a very nice subset of Scheme. However, I'm coming to find projects in Python relatively hard to maintain. :-/ I feel that when Python projects hit a certain size (when a program reaches something like ~20 non-trivial classes, with some inheritance or interfaces, something like that), it becomes hard for new comers to extend it successfully. It may be just me, but I find that the lack of a canonical way to do things like interfaces means everyone has their own adhoc way to do this and ... things just get messy, or at least more messy, faster, than they do in the other 3 Google languages. It could also be the lack of type checks at compile time, I'm not sure. But I digress, all I meant to say is that I think Go may actually make things a lot better than Python in this regard, so I'm starting to use it in this area.