If deposit 1 billion, broker give-me 2 billions? There is any absolute limit for margin buy power ?

[ironchef]

Ouch, sorry to hear that.
Citigroup is up 3% today, if that's any consolation.

That is OK, you win some you lose some.

For every C I have one up 10X, like BRK.B so it all balanced out. However, I often wondered why not just buy SPY and QQQ?

Holding names is more fun, you have the illusion of real ownerships.