The MtGox head opened a US bank account under false pretenses. After FinSEC published their guidelines he failed to come into compliance, presumably based on the assumption that the Mutum Sigillum intermediary was enough to insulate him from prosecution. This prosecution was inevitable.
This action will put the fear into other exchange owners, who will now either shut down or come into compliance.
End result - legitimate, insured exchanges available to the masses. Bitcoin becomes ready for mainstream adoption.
No wonder so many VC's in Silicon Valley are pissing their pants with excitement!
I agree this will only force other exchanges to comply with existing laws which can only be good for Bitcoin.
Why should it be good? When crypto currency exchanges start to be regulated by the FED than they will introduce restrictions, taxes, etc.
When the government brings regulation into an industry / sector etc.. it also brings legitimacy which brings trust which increases adoption etc...
I don't see why regulating exchanges would be a bad thing - for example the SEC regulates the stock markets in the US and most of the rules they enforce - like insider trading - are meant to protect investors not the exchange. For example imagine this.
1) I create a new coin called the XYZCoin and premine it.
2) At the same time I setup an exchange which trades XYZCoin.
3) I prepopulate the exchange with a couple of fake trades showing that XYZCoin is worth $0.03 or something. Maybe I put ''Trades might be simulated' in fine print somewhere.
Who's to say that the coins aren't worth $0.03? What if people actually sign up to trade and somebody purchases my premined coins? What if after I sell my coins I just shut down the whole thing?
This is why regulation is needed - things like this, you shouldn't be able to create a virtual-currency and then turn around and run / influence an exchange - it's a clear conflict of interest. You can't report that a virtual-currency traded at a value when it hasn't. Right now I don't even think a virtual-currency like Bitcoin has legal status so it makes it impossible to enforce any existing laws (like theft).
As for taxes I have no comment
The US takes it's tax laws very seriously so, yeah, you should always pay your taxes if you live there. I might be mistaken but I think that you only need to pay taxes on something like Bitcoin when you convert to USD - assuming you live in the US. In theory if you never converted to USD then there would be nothing legally to pay taxes on.