GM Secrecy and Metagaming

[JMD]

One of the big things I noticed upon switching from DnD to GURPS about 7 years ago was the lack of any sort of monster compendium. An interesting byproduct of this is that my players, all of which own the DnD monster manual, no longer knew what sort of being they were facing. They went from a world where they knew the powers, stats, ac, and damage of every monster (or least the general idea from seeing its entry) to having no clue as to what they were facing.

This is mostly fine. The mystery is pretty great and keeps them on their toes. However, the players no longer knowing the monster forces all the math onto the GM. "I hit for 14 impaling, armor divisor 2, 4 burning follow up." The GM, if he didn't reveal the monsters DR, is now stuck mathing that out, nullifying the autocalculation feature of many GURPS aids and sheets (such as the GURPS Calculator, have you checked it out? It's insanely amazing.)

What's your policy on keeping the statistics of monsters secret? What are the pros and cons in your opinion?