My current balance stands at $30. Originally I was going to put $20 in the account, however a promotion was offered stating that if I put in an extra $10 I would be credited $100 as well. Looking at this now, I do not see any history of the credit.
Re: Current balance
When you enter a promotional code for spend X get Y, you would actually need to fully 'spend' the allotted amount before the credit will be added to your account. For example, in your case you would need to accrue $30 of advertising costs before the credit would be added (rather than just adding $30 of credit to the account).
Hope this helps.