Speaking of mistakes, "Biggest mistakes you've made with bitcoin"  

Pre-Ordering bASIC's. Lost nearly $100,000.

Ouch. sorry about that.

Selling cheap :|

Not selling at $266...

Ouch, that stings, my sympathies man.

Yes and you know a lot of people did just that and are laughing now (and rolling around in their pile of money). 

I used Bitcoin 24 (who was the largest exchange for EUR at the time) and had 45,000 EUR worth of BTC + fiat on it. Withdrawals were taking too long.
Then I learnt that it was a single person operation and the owner is a german DJ. Then I found what he posted on stackoverflow, especially this gem: http://stackoverflow.com/questions/15026825/php-mysql-how-to-prevent-two-requests-update

Still waiting for my BTC + fiat, not much hope though as you can expect

Not buying some when I first heard about them.
Tried mining on my normal PC back then, it didn't create coins after a whole day.
Yes, I thought mining them was the big deal and didn't know anything about the 21 mio limit and so on.

-> If I had spent like a day more reading about it, I would have spent a small sum (I guess that would have gained me ~100 BTC).