I'll just comment that not all grey sheet/market stocks are the same.
The stocks that drop to the greys due to SEC suspensions should be avoided without exception.
ADR, or foreign stocks trading on greys are another matter. However, I wouldn't consider trading them since getting in and out can be difficult at times. I'd only invest if looking to hold long term. I'm holding one at the moment that I bought via Fidelity. You usually have to look at the foreign exchange to get an idea of where they should be trading, but, the grey market volume is quite a bit lower than on their home exchanges. It's that low volume that can be killer. You need to do limit orders.
GLTA... KarinCA ;)
"Be kinder than necessary, for everyone you meet is fighting some kind of battle."