This has been debated again and again, but remember, Joel is a business guy, not a software guy. He clearly knows nothing about type systems, so anything he says about them can be ignored.

(BTW, CL is dynamically-typed, but runs as fast as many statically-typed languages. Typing helps the compiler generate fast code, but if you have machinery to recompile your program as it runs, you can decide on the type at runtime rather than program-authoring time. Ruby is slow because its implementations aren't very good, not due to any intrinsic property of Ruby.)