One thing I struggle to understand is how common lisp deals with the "modern" multi-core world. Not just "async i/o" - that's just the tip of the iceberg - but concurrency in general.

I know that common lisp (the spec) explicitly doesn't mention any of this - it was the early 90's so who cared anyway - but how would you fit common lisp into a modern server-side app that has to process many things at once? Or is that just not an area that it's concerned with?