I don't mean to say that BTC is useless in a hostile environment.
However, a popular idea with any new technology is that it's going to be so new and so different that the legal system can't possibly understand it or deal with it.
That might have worked 20 or 30 years ago but not any more.
There's always a lag between the development of a technology, the adoption of the technology, and the regulation of the technology. Nobody bothers regulating things that aren't used, and things can't be used until they're developed. So the law (and the tax man) will always be a little behind the curve.
Witness the people squealing because Ebay and Paypal are now reporting transactions to the IRS. A lot of people were apparently unable (or unwilling) to distinguish between the reach of the law as an abstract ideal and the on-the-ground efforts of enforcers. They thought that because IRS didn't have an easy way to track Paypal/Ebay transactions, that they were somehow untaxable, or effectively immune from taxation.
I've seen statistics (don't know if they're true, to be honest I'm suspicious) that in some places Facebook is mentioned in divorce pleadings by one side or the other at a > 50% rate.
BTC will get there, too, if it turns out to be even modestly useful.
From a literal point of view, I'm not sure it would help Kim Dotcomm that much if he did have assets squirreled away as BTC or on one of the exchanges - I haven't followed every twist & turn of the case, but I gather he's still in custody and probably has no Internet access. All of his computer hardware has likely been seized and powered down, either by law enforcement or by service providers that aren't getting paid.
Even if, best case, he had a paper wallet or a brain wallet with a lot of BTC in it, he'd need to give that information to a trusted person who would then access the funds on his behalf. Or maybe the trusted person just runs for the border once they've got the cash.
It's not like Kim is going to be hunting them down for revenge any time soon.
The US law enforcement community has a lot of experience with tricky defendants from all of the drug cases we've seen over the last 30-40 years of the "war on drugs" - prosecutors can and will go after defendants' funds as the fruits of (or evidence of) wrongdoing, effectively denying defendants meaningful assistance from competent counsel. I haven't had that happen to me personally but it has happened to attorneys I know well and it's scary - the attorney's role can flip from advocate to co-defendant basically at the whim of the prosecutor.
And then there's the http://en.wikipedia.org/wiki/Lynne_Stewart
case - I don't know whether or not she's guilty of what she was convicted of, but you can be sure that criminal defense attorneys are aware of that prosecution and are going to be very careful about proposed transactions from in-custody defendants who say "well, give this scrap of paper to my assistant" or "use this information to get my secret BTC stash" or whatever.