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?