Is this a dangerous thing to put on ones website at all?
What kind of danger are you thinking?
The exchange could also go under and/or rob you. You should be careful about to whom you give your bank account numbers.
My guess is he's referring to one of the many "dealers" that were hacked and had bitcoins stolen.
Similar risk to cash in the mail, except with cash in the mail there's nothing you can do to protect yourself (or prove that delivery was accepted.)
If it's $20,000 cash in the mail, it weighs about 200g (100 $100's) and to mail it about an hour from here (1 hour 30 minutes by car) Rochester to Buffalo, registered mail with $25,000 insurance, flat rate priority mail envelope is $53. I guess that price is the same across country.
OK, so it's actually cheaper to mail cash than to trade bank dollars for bitcoins. I'll get off my pulpit now.
(PS: I'm pretty sure you actually have to pay taxes on that cash you received by mail, especially if it's registered and insured, now that it's yours, it's income. Bitcoins on the other hand are not cash. I am a newbie to taxes, but I don't think you would have to pay tax on bitcoin income unless you were actually cashing them out. Maybe capital gains. Any experts?)
And then, only if you actually cashed out, right? If you leave them as bitcoins and the value drops below what you paid, now you've got a loss and maybe deduction instead...
It would make sense that you should pay taxes on mining income (if they can find you).
Most people earning income in bitcoin probably aren't doing it by mining, especially after ASIC arrives. Just to point out that mining is only one of many ways to earn bitcoin income.
I am not so sure that ASIC will kill the small-time mining scene, the low-end ASIC miners are cheaper and less power hungry than video cards (though you can't play games on them), it will just mean that if you want to mine bitcoins, you'll have to get one (or more), and you can't rely on your video card anymore. So a lot of people will be pushed out.
Bitcoin exchanges are not like Paypal, it's a terrifically bad idea to keep your coins in a wallet controlled by a third party for any length of time.
Local wallets are easy to keep secure. Just keep it on a flashdrive, don't let it touch your harddrive, and don't use it on a pwnd computer. If you want, you can even keep that flashdrive in a real bank.
But the evidence seems to show that the track record of bitcoin accounts kept by individuals is significantly worse. For instance, http://arstechnica.com/tech-policy/2012/10/78-percent-of-bit... and I think I am safe in concluding that a significant portion of those "non-circulating" bitcoins are actually lost.
So my financial advice would be that you are better off trusting an exchange than trusting your own storage and backup procedures.
Maybe you have found evidence of an elaborate ponzi scheme that we are all played by, but I don't buy your conclusion, and it's not the conclusion of the linked article.
If only 90,000 bitcoins held by/moved through a small group is driving most of a total of 423,000,000 bitcoins transacted, then I'd say the rest of the owners of the 9mil bitcoins in existence owe those guys a debt for stress-testing the grid.
You can use a cloud bitcoin wallet, like BitcoinSpinner, which is implemented on top of the BCCAPI. While I have not read the actual API, and I'm not sure this program is open source, I can tell you that it promises your bitcoins cannot be stolen from the cloud!
If that's not good enough for you, and you don't trust your own safe box in your own house, then I'd suggest you run back to your FDIC insured bank, or better, start reading. It's shameful to hear Hacker News readers saying they don't trust their own data to stay safe.
Look, I am a reasonably skilled programmer, and I work for a bank. I know a great deal about keeping data safe and keeping it backed up well. I have written simple cryptography algorithms for addressing these sorts of issues (like secret sharing). And I know enough to realize that these are HARD problems, and leaving them to professionals works better than thinking you are smarter than the rest of the world.
As an example, it sounds like you store your bitcoins in a safe in your house. Nice system... I'm going to assume that your safe is fireproof, and that you were careful about not storing the data elsewhere. Now here's a question: if you die, will your heirs know how to retrieve the value, or will it be lost forever? Those are the sorts of hard problems that an institution can probably handle better than you can.