There are some very good interface for interfacing the PC - USB to DMX using Atmel AVR's. I personally have successfully built and use uDMX 1.2 USB-DMX Interface http://www.anyma.ch/2007/research/udmx-12-released/
. Atmel AVR's are cheaper than PIC's in this part of the world ........
but I personally love the PIC's.
Microchip's new USB driver chip seems promising and very simple to use. Its also cheaper than its rival FTDI chips.
I was just thinking if anyone would be interested in cloneing the Enttec - Open DMX USB Interface using this chip.
The hardware could also be a generic USB <> RS485 bridge, not necessarily for use in DMX.