Homebrew PCBs

I just tried drilling a PCB before exposing it, and it didn't seem 
like a better method.  Spinning carbide drills at 30k rpm, the green 
photosensitive coating flaked off near the holes.  Just like sheering 
the boards before exposing them.  So, I think for the near future, 
I'll expose, develop, etch, _then_ drill.

Does anyone know for how long they are photosensitive?  Are they 
still sensitive after develping?  Do I have to etch in the dark?

Thanks!

- Steven Ciciora