0/conf will work for retail transactions. I bet the rate of people using a double-spend technique to screw people out of money would be roughly equivalent to the rate of people using counterfeit bills for a cash transaction. And whoever the retailer is can use security cameras or other techniques to track the perp down and prosecute them.
Plus, with online wallets like MyBitCoin, if you trust them and their API, you can have 'instant' transfers and all payments can be forwarded to a different address so I think the practicality of instant payments can be solved via the market even though there is the problem built into the BitCoin software. Heck, banks do not settle for over 24 hours with leads to Herstatt risk (after the German bank regarding settlement risk issues and time zones).
I can imagine markets where instantaneous confirmation would be absolutely crucial. Less critical when you can delay shipping something physical via mail, or offering the client who just bought that mega flat screen TV a coffee and a seat. But how about prediction markets or betting exchanges settled in BTC? Here the counterparty wants to know immediately if the deal will go through, otherwise the price might have changed once they realise they need a new match on the exchange for their deal.
I don't understand how that proxy-bitcoin concept would work in reality - either it is doing the same thing as Bitcoin and is slow, or I have to trust it (for small amounts) and then I could simply use small Bitcoin transfers?
Somehow banks delaying payments for 2-3 business days (for technical reasons, if you are one of the many dud banks with ancient systems, or because you just happen to like your free lunch:) should not be the benchmark for Bitcoin. Wasn't the key concept that it is a lot faster (as long as you need to be convinced by confirmations) and doesn't require specific trust in one specific, reputable 3rd party (like Mt Gox or Gavin), only the nodes?