so what is the common use case for using Node, and what in that use case eats CPU?
The article mentions that using NodeJS as a simple HTTP proxy with no application logic can sustain only 2100 reqs/s before a 2.5GHz Xeon is maxed out. NodeJS uses CPU more efficiently than other HTTP stacks, but its I/O engine is not infinitely scalable.
That sounds fairly lame to me. Proxying network traffic isn't a CPU heavy operation. Worst case you have to move a few bits of memory around.