As an experienced retail trader and python hobbyist I still have to discover quantopian's true usefullness. So far ... I only discovered the limitations ... no offence. I think people with limited or no real trading experience will have a hard time making real use of quantopian ... or any other similar platform anyway ... no offence again :)

I agree with Grants point that institutional traders have access to much better tools, however, they have limitations that they must carry the cost of these expensive tools by only playing in highly liquid markets. Quantopian still lacks a lot of things but it is moving quickly. One example is the history feature. Although it's still new (read, not fully implemented), what is there has allowed me to do much more that I was before, with very little work. Tools like this can snowball to a point where suddenly we are on a level playing field. I just recently completed work on my first workable algorithm, and I've just started paper trading. So I share Grants frustration, but at the same time, I have an algorithm working now, and when I first started, it was out of the question. I feel that within a year, I'll be trading real money.

I think the Quantopian guys need to concentrate on those things which can make people successful. Here are two things which I would like.
1. A library of sample algorithms which actually make money. This will help people get started and inspire people to do better. Many beginners would love (pay for) the ability to have trading algorithms which will trade their own selected stocks. Others would like to have algorithms to rebalance etfs. There are plenty of web sites with systems which do this, but they make you place the trade. I think it would be worth it to hire an experienced quant to do nothing but but these systems together for a few months. I believe there is a huge market of people who would like to trade while keeping a day job, and quantopian can be a solution if it offers the right help. Some people will come up with a better mouse trap, but the bulk of people would be happy to be able to select from and perhaps tweek an existing mousetrap.
2. I am held back, and I think others are also, by not having indexes available with the trade data. I personally need the vix and vxv, but there are lots of other things people need. Take a look at the market indicators from stochcharts.com at this link.
http://stockcharts.com/school/doku.php?id=chart_school:technical_indicators
Yes. I'm getting around it by using fetcher, but that means I can't get fresh data during the day, and I also don't trust it for live trading. I also don't know when the data is available. If I fetch during the day, is it yesterdays data, or do I get data from the opening? I'd like to get the data from the history feature.

One additional comment. The reason I am interested in Quantopian, rather than the host of mature products which are out there based on PC software, is the promise that I won't have to do all of the technical work to put together all of the pieces of a system, and then to maintain it. I would like to develop and trade algorithms, but I don't want to commit the time to maintain such a system. If Quantopian can meet the promise, I'll be very pleased, and won't mind paying a reasonable fee for the services. For me,$100/month doesn't sound unreasonable for me if the platform is reliable and trouble free because I trade larger accounts. I do think it could be nice to have a lower fee for small accounts. Although there are features like optimization of variables which would be nice, I don't think that is so important, since I can do it by hand in a few hours if I'm thoughtful about it. If I can program at night and have the algo's run during the day, I'm a customer. I'd also like a marketplace, so I could buy and sell code.

Thanks Richard,

Admittedly, I don't have any experience with trading, so perhaps Quantopian is offering something valuable. However, at this point, it feels pretty incremental and conventional, trying to grab a share of an existing market rather than create a new one. As a start-up, my sense is that they need to be careful and "keep their eye on the ball" and not just try to attract experienced users from other platforms. For me, it is hard to tell if they are still looking to unconventionally "hack Wall Street" (and I think that they are funded by Wall Street folks, so this could be a tall order). In other words, what is fundamentally different here?

Grant