As far as I'm aware, Mt. Gox is the most secure exchange around right now and hasn't had an incident since its big one last year. Even so, you only have three fears: 0) You poorly secure your account and someone logs in as you and takes your coins 1) Bitcoin's value plummets and you lose all your invested money. 2) Mt. Gox loses some of their actual coins, and refuses to let you withdraw from your balance with them. 0 and 2 are theft, which is a constant concern to anyone regardless of what is being stolen. While I don't think Mt. Gox insures any of its deposits with something similar to FDIC insurance, I bet there's an insurance company out there that will insure your bitcoins for a fee.
Also, it's easy to get rid of #0 as a fear. Does your bank (or more analogously if you have stocks, your account for some company's online trading interface) support YubiKeys or similar? http://www.yubico.com/ Mt. Gox has given quite a few of them away for free. (Mine was free.)
I have a fourth fear with Mt. Gox. For a European the only way to directly buy Bitcoins there is a SEPA transfer. Mt. Gox will only accepts this after I send a scanned identification document and a proof of residency without ANY alterations.
I understand why they need this and I appreciate that they are thorough in their measures to prevent fraud and money laundering. I even sent my passport to other companies, but only altered in a way that makes it unusable for identity theft.
But still: I don't trust them enough that I don't fear my passport scan gets leaked some day and is used for identity theft.
I worried about the same thing about sending something that exposed my Social Security Number. So I submitted my driver's license and car insurance policy for identity and residence respectively. (It was kind of a pain to find a proof of residence they accepted since I had no bills in my name.)
For anyone browsing the thread, this is part of an email their support desk sent me for accepted documents, which is significantly more permissive than the upload page for verification suggests:
1 A copy of your government issued photo ID such as:
- Passport
- Permanent residence card
- Driver’s license
2. Proof of Residence that is not older than 3 months such as:
- Monthly utility bill
- Internet Bill
- Cellphone Bill
- Tax Return document
- Residency Certificate
- Voting registration form
- Medical insurance
- Pay Slip
- Car Insurance Policy
- Medical Bill
Also, it's easy to get rid of #0 as a fear. Does your bank (or more analogously if you have stocks, your account for some company's online trading interface) support YubiKeys or similar? http://www.yubico.com/ Mt. Gox has given quite a few of them away for free. (Mine was free.)