Mybitcoin accept with 0 confirmation?

[BITLISH]

Hello eveyone,

I want to start accepting bitcoins in my shop and like the idea behind mybitcoin - instant confirmation with their sci interface.
But no matter how one transfer the coins - either mybitcoin wallet or home bitcoin software - it confirms transaction instantly, without even 1 confirmation.

Mybitcoin support keep silence (that worry me too). So my question is: Is it safe?
What about double spending? Is there any kind of chargebacks on mybitcoin?

To make myself clear, I imagine following situation:
someone transfer to mybitcoin, this transaction accepted without confirmation and coins can be and will be spent right away.
What happens if after the first block, this transaction become invalid? My best guess is that mybicoin will deduct this amount from my balance, and that is unacceptable for a shop.

[Stephen Gornick]

What happens if after the first block, this transaction become invalid? My best guess is that mybicoin will deduct this amount from my balance, and that is unacceptable for a shop.

Ok, you want to accept payment on 0/unconfirmed but you then want a guarantee against a double spend?

Unfortunately, the choice will boil down to either you accept the risk or you wait until one confirmation (or more, depending on the type of transaction).

Here is some more info:
 - http://forum.bitcoin.org/index.php?topic=27417.msg350531#msg350531

[BITLISH]

Unfortunately, Mybitcoin.com doesn't have any tunable value for number of confirmations.

So I want more confirmations, by mybitcoin doesn't allow me to do that.

The choice is whether to use mybitcoin (very handy for clients), or not.