Peter McCormack has mentioned a couple of times that he's postponing (or considering it?) his tax payments so that instead of paying x amount of BTC's worth now he can pay them a fraction of x BTC's worth at some later point.
Apparently in the UK, if you don't pay your taxes on time, they'll send you reminder letters and you can postpone it for a long time without serious consequences, like hefty fines. The worst they will do is add some meagre interest.

So postponing your tax payments is effectively an interest-free or low-interest loan from HMRC (if you believe you owe them anything to begin with) you're guaranteed to get, regardless of your credit history.

It's a speculative attack on fiat and its mispriced discount rates. Discount rate arbitrage.
They think the 5% or whatever interest they're charging you is a lot and that it's enough to scare you into paying on time; little do they know...

I've applied this approach myself in a more softcore version to two things recently:

1. My water bill.
   I used to pay twice a year - in March and September, for 6 months up front. My next bill, £267, was due by the end of this month. I looked at the water company's website yesterday and found I could switch to monthly payments. So I switched to paying monthly, which compared to the semi-annual payments was like a zero-interest installment plan. Not only that: the first payment I'm due is on May 1st! So no water bills for me for another 6-7 weeks.

I don't need to tell you where that £267 went.

2. My mortgage.
   I had made overpayments on my mortgage a long time ago and had forgotten about it. My mortgage allows me to underpay from the overpayments made in the past.
   I was due a payment last week. The day before I called the lender and arranged an underpayment, and ended up not paying at all this month. It means my monthly payments will go up a bit in the future, but at the 3.39% interest rate it was a no-brainer.

An extra £770 not debited from my bank account and exchanged for you-know-what.