I built the Thien lid yesterday and it's quite amazing. I filled a 30-gal steel can halfway with dust and chips, shavings, and nails and debris from the floor, and only a handfull of dust got to my 2-hp HF's plastic bag.
It's Phil's original plan but with 4" ducting using the new screw-on fittings from Rockler. I also tested with a Ridgid vac with a reducer on the lid inlet, and it worked great that way also (in fact, the vac dented the can).
I want to thank Phil and dbhost for plans and assistance.