Here are some of the main practical reasons I didn't sell:
(1) I don't trust the exchanges, or any 3rd party, with my bitcoins.
(2) There are possible (negative) tax consequences to moving in and out of bitcoin on exchanges
(3) There are additional, and as yet unresolved, tax consequences to withdrawing significant sums of bitcoin, especially to US bank accounts.
(4) There are yet potentially more (negative) tax consequences to using non-local exchanges as a US citizen.
(5) If, in the US, I'm merely subject to capital gains, my tax rate is significantly reduced by holding my bitcoins for more than a year.
I've engaged an attorney and a CPA to work the details out for me, because it's actually quite complicated. US citizens goofing around on foreign exchanges with sums of money the IRS would care about are playing a dangerous game, IMO.
Finally, I'd simply prefer to keep my bitcoin wealth in bitcoin and spend bitcoin for the things I want/need. I've been in the market for a new vehicle or two, and now that there are a couple of dealerships in the US that sell cars for bitcoin, it's preferable to take care of that transaction without liquidating on my end. The tax consequences are simpler to work out (at least right now), and greatly reduced on my end by simply spending bitcoin.
I am very interested in all of this. Anyway you could make a thread when the attorney and CPA get back to you? I wasn't even aware of (4). Is that an additional percentage?
I don't really know how it all works, which is why I've hired somebody to figure it out. What I do know, so far, is capital gains is the ideal scenario, but there are still a lot of open questions. If you're in the US, and you're trading on foreign exchanges and withdrawing USD (especially atypical/large sums), and you're not personally equipped to work out the tax consequences of what you're doing, then you're playing a dangerous game that could come back to bite you later.
I'm not saying don't use foreign exchanges. I'm simply saying that if you think you can simply buy bitcoins on exchanges, and magically come to possess the results of appreciation and use it without any accounting, you are ignorant in a way that could cause you some pretty serious problems in the future.