NEVER send your privatekey into a website!!!!! Even sending your privatekey in the clam client i find tricky, sorry.
Sorry for bumping, but needs to be said.
Just-Dice is a fairly trustworthy site. More importantly, I made sure to withdraw coins from the address before entering my private key. Since then, I've only had a maximum of $10 stored in that address which should limit the damage in the event that JD is hacked or goes rogue (yeah, I know it's better to stop using it completely).
JD once held over $60 Million worth of peoples BTC..
The owner dooglus is about as honest as they come.