They're popular in the CNC world, yes. For instance, the recently Kickstarter-funded MyDIYCNC project also natively interfaces through the parallel port; Stephen McGloughlin, who's behind the project, is building an USB interface for it from scratch.

The main issue seems to be the timing with controlling... parallel i/o lines. From http://www.cnccookbook.com/CCBreakoutBoards.htm :

While there are boards the purport to simulate a parallel port with a USB connection, most of them don't work for CNC applications. The reason is that they are not high enough performance to maintain the exact timing relationships needed to produce a clean pulse train to control multiple servos or steppers.