Right, so if you cannot write solid C code, don't use a C based Ruby runtime, because not being able to write a fast library if need be cripples you as a programmer.
I don't know if it cripples you but it certainly makes the problem domains that you are going to be able to tackle effectively smaller. But a lot of the time you are going to get the most speed improvement by just looking for an appropriate algorithm.
Sure, and when I have chosen a good algorithm, I want to implement it in a language/runtime that is suitable for algorithmic code, not in Ruby or Python or PHP. To be able to do that is something I expect of myself and everyone I work with.
It's obviously not a formal distinction. Algorithmic means "spends a lot of time running loops doing something interesting" as opposed to "copies data back and forth between the UI and the DB". Or CPU intensive versus IO intensive.
[Edit] And just to be completely clear and also reap all the downvotes that I can get from disgruntled web devs: Python and Ruby are indeed totally unsuitable for writing CPU intensive, complex algorithms. If you write Ruby or Python code, avoid loops! Try to be declarative so all the loops stay in the C code.
