Ruxum posted here
earlier looking for testers. I have an account, and I love the interface. It gives me instant calculations for the fee and cost while filling out an order, and it has the chart and order book on the trading page for quick reference.
One thing it lacks is a good way to withdraw and deposit small amounts of USD. The only currently available method is bank transfer that costs $10 to deposit and $25 to withdraw. They do state that more options are "under consideration," so this may change.
They also hint at a "Ruxum Pool" that can be used to fund your trading account.
Yeah. The only thing that will kill it (and it's been said here a few times) is easy-in/easy-out of money. BTC is already difficult enough for the mainstream to understand. If it's too expensive and difficult to get your money in and out, then it's going to have major difficulty growing.
Look at any other exchange in the BTC world where their ins and outs are messed up (BTC7 springs to mind). Prices stagnate.