Sybil is a real pain, and HashCash (via I2P, which had it as an anti-DoS option) was the first obvious attempt at a solution that worked. It would be better done with Argon2 now, but it still burns coal and is a bet that evil nodes don't have more power than all the good nodes put together - it seems we aren't always going to win that bet.

Will proof-of-stake would be any better? It doesn't feel as suited to things other than currency to me, because: what value does the deposit have? We'll see how it turns out when deployed, it's hard to predict how people will react.

There's a surprising amount of heat in the field now. Lots of activity, like this interesting work, some very strong opinions. Please don't eat me! I'm quite happy to leave it be and move onto other things.

The more power consumed, the stronger it is. A cheap chain is a weak chain

How about solar batteries with built-in "greencoin" cryptocurrency mining circuitry, that generate electricity instead of heat as a by-product? ;)

Check out Safecoin, http://maidsafe.net/documents

Ethereum is going to do that in about a year.

can you be a little more specific?

TL;DR. What's the takeaway?

Instead of a hashing contest it uses time locked deposits on which block will be accepted next.

To my understanding it works out as a combination of prediction market style betting and bidding for a block to be accepted.