I've not seen any way to resolve the problems with my original proposal; it seems too easy to use a large amount of cash to reach back arbitrarily far in the block chain to re-write history (and hence, invalidate transactions where you spent money).
... or, even worse, invalidate competing proof-of-stakes.
I might like proof-of-stake schemes better if somebody has a good plan for how to get them started-- you've got a genesis block, so the creator starts with 100% stake.
Now what, exactly, happens to create block number 2 for proof-of-stake systems?
Sorry for the late response. Subject to temporary ban for trolling libertarians.
Gavin's question about the initial distribution should not be a sticking point. There are many possible answers. Here is one.
I suggested that mixed proof of work and proof of stake may be a promising option.
In a mixed work-stake implementation, the initial distribution system could resemble other cryptocurrencies. Proof-of work could operate similar to bitcoin, with the key exception that difficulty criteria would be individual specific. An individual's target difficulty would be a decreasing function of that individual's stake. However, system rules would specify a finite difficulty target even for individuals with zero stake. Initially, there would be no stakeholders, so everyone would share the same difficulty target. Over time, people would accumulate stakes based on their historical mining and trading behavior. This would generate inequality in difficulty targets across individuals. Stakeholding would then become an important determinant of mining ability.