I've been using it, and promoting it. The opportunity for arbitrage is real, the numbers and deltas are factual. I'm keeping a blog update at
http://notnull.org/bitcoin-arbitrage-news/bitcoin-arbitrage-updates/ and in the event I get screwed, which would really only be if they steal and bail, I will certainly be posting. But there is little reason too, there is far more upside to stick around and continue the arbitrage strategy, the difference between the markets is significant, and consistent.
The idea of an annual return, assuming 2% every single day, is huge, but it won't be 2% every day. Yesterday it was 2.28% and a couple days prior it was .4%.
It's just logical math, if it's a scam then the joke's on me, but I sense the trolls are just jealous and so jaded now after Gox that any investment with any promise is too scary to consider objectively.
It's not just the massive profits they claim to make. It's also the question
As you said, even a reasonably small investment of their own would allow them to make loads of money for themselves... but for some reason they don't want to do that, and instead give you the guaranteed profits.