Just use BTC or satoshi (0.00000001) like in:

I just bought a car for 10 BTC!
The new Final Fantasy game will cost only 15000 satoshi!

Using mBTC, uBTC, μBTC is just unnecessary, sounds like a different coin and it will confuse a lot of people.

Coinedup and a few other sites are guilty of using mBTC.

1 satoshi is the smallest unit of BTC that's all people should have to learn. If you want massive user adoption you have to simplify things.