InclinedPlane, your anti-deflationary arguments can be refuted in 4 different ways:
1. A deflationary currency strongly encourages businesses to maximize revenues today instead of tomorrow, because they know they can get more units of the deflationary currency today rather than tomorrow. This incentive does not exist with inflationary currencies.
2. If you had 100% confidence in Bitcoin being deflationary, you would invest in bitcoins. But the fact you do not (I presume) shows a very important point: you, like many, doubt Bitcoin will remain deflationary on the long term (eg. it might crash to zero). This uncertainty is why, despite being in theory deflationary, Bitcoin will continue to see a growing economy. People will continue to invest and spend bitcoins, because the future of Bitcoin, like the future of any currency (inflationary or deflationary), is fundamentally uncertain.
3. There is an often-cited counter-example to the argument that "people will not spend if they know prices will decline in the future" (as prices will in a deflationary currency): the electronics industry. Laptops, smartphones, servers, etc: prices are always decreasing. Yet this industry is very successful. Buyers are not afraid to spend money today, even if they know they can get the product for less tomorrow. This is because prices decreasing over time stimulate spending.
4. The traditional arguments against a deflationary currency only work within a self-contained economy anyway. Bitcoin currently exist as a side currency next to all other (USD, EUR, etc). People will still want to invest these currencies, and the Bitcoin economy being tightly coupled to
others will naturally benefit from these investments. That's why for example we are seeing a bunch of Bitcoin startups popping up: Coinbase, BitPay, BitSpend, BitcoinStore, CoinLab, etc
Edit: downvoting me, seriously? I would like to know why.