Far Manager is the only thing I miss after switching to OSX 6 years ago. Tried Midnight Commander and other alternatives, but not nearly as good imo. File search is the killer feature, so much better than any other alternative.
You would trade them for gbp/usd on one of the exchanges. Mtgox.com is by far the biggest.
As for tax, this is probably taxed as any other profit you make on buying and selling stuff, at least in my country (Norway). If I buy an art painting and sell it with a profit, I am obliged to inform on this on my tax sheet. And the same goes for bying/selling other currencies as well, but bitcoins are harder to track for the government (but not impossible).
We're actually building an MVP for a similar site with focus on the market in northern Europe, it would be interesting to hear where it went wrong for Loosecubes. They looked like the best kids in class.