My Bookkeeping Mistakes

Here are a few mistakes I've made in accounting:

Not photocopying checks / deposits before making the deposit. Later, when looking at the statement, I can remember that several items were included in the deposit, but I couldn't remember the break down.
Counting income twice. This was a dumb mistake on my part. I would recognize the income when issuing an invoice, and then also count the deposit as revenue. In the first place, I matched the revenue to accounts receivable, and then debited accounts receivable when the payment was deposited.