It needs some kind of incentive to get people to sign the checkpoints.
PoS is better than relying on one developer to lock the chain.
This is a fair point, however it doesn't allow the masses to participate. Therefore for all practical purposes, one tyrant or a few oligarchs results in the same situation. At least you can talk to a tyrant. Oligarchs are paranoid fucks who need to be spoonfed incentives.
The incentive is: it keeps their (bit|lite)coins from becoming worthless. When you have or control a significant portion of the total supply of coins, that is no small incentive.
The checkpoints also affect low stakeholders. In an effort to gain more control, high stakeholders can pay for attacks (including psychological) which create chain forks that send money from low stakeholders to them.
Incentivism is a futile exercise in trying to motivate the lazy. There's an undercurrent in the bitcoin and litecoin communities that will throw off the dead weight of fat wankers who need an incentive to tie their own shoes never mind create.
So far those proposing proof-of-stake have failed a simple test:
I haven't heard of one proposal that allows pools of peasants to be stake miners. Effectively these would function as cryptocities as there would be an incentive to keep cryptocoins within communities. This would create feedback loops and self-propelled microeconomies.
It was a simple extension that never crossed anyone's mind. Fail.
Failing this simple test does not give me confidence in proof-of-stake models. The people looking to add this feature are still thinking in terms of maintaining value rather than creating value. You guys are not thinking forward and it scares me to death.
There's a thread here that is going to cover the whole gamut of proof types that could make cryptocurrencies work.
http://litecoinforums.org/index.php?/topic/22-cartel-wars/