(...) Bitcoin is not deflationary. Right now inflation is still over 25% yearly, and in December it will drop to about 12%. That's still very high inflation short-term and mid-term. The question is how many people hoard, and what are the effects of the long term ~0% inflation, and also the fact that the underlying bitcoin economy might be growing faster than money supply right now.
But "deflationary" is a misleading word to describe bitcoin's planned money supply.
Well, we have 25% inflation if you define the word 'inflation' solely in terms of the coin supply. But the normal meaning of 'inflation' and 'deflation' is related to how prices change, and in that sense we can say there is deflation now in the Bitcoin economy. This is because the user base for the currency is expanding quickly and people are willing to pay more and more fiat for a bitcoin. Since most products and services sold for bitcoins get their price by converting the expected price in fiat currency, things have been getting cheaper in BTC.
Thing is, inflation in that sense doesn't translate well since most prices are decided in terms of whatever the exchange rates are against fiat references. We have no significant price indices that are native to the bitcoin economy and the exchange rates are highly speculative and volatile.
The inflation that matters for trusts, banks and funds to be able to return a given %APR is mainly defined by M1 and M2, which also define consumer prices for established currencies.
The pizza that was sold for 10,000 BTC in 2010 would be worth around 2 BTC now. That's quite a deflation rate, and I expect that trend to continue during the next years.
Considering the volatility that would be a risky bet for any given point in time. The pizza that was sold for 10,000 BTC in 2010 would be worth 0.7 BTC in July 2011 and 2 BTC now. Because pizzas are priced in fiat, not in bitcoin and they won't be priced in bitcoin any time soon.