PoS being sound enough to actually work despite warnings from nearly all competent analysts, go right ahead. And I really do mean this. Being willing to go up against the prevailing wisdom of experts is a great thing and important to progress. Just know that the odds are very much against you.
But there are experts on both sides. Vitalik just recently being a convert. And SlipperySlope here as well.
I know gmaxwell has posted about 'Nothing at Stake' attacks, but that appears now to be a solveable issue. Infact, Vitalik wrote a whole article about them and it appears as a result of his article sparking debate, a solution was found.
I certainly don't claim to have the anwser, but it would appear that this is something that's headed towards being solved. Unless of course AnonyMint is correct and it's totally unworkable.
If it comes down to one entity controlling 51% of the money supply and that's the main issue, then I think it's already better than PoW since theoretically it should cost more to mount that sort of attack than attempt a similar 51% attack on a PoW network(edit: unless someone can borrow 51% of the money supply on leverage). If there are other issues then of course all of those will need to be solved.