Edit (12/15/2015) - I wrote this awhile back when Robinhood was first launched into an Open Beta. I'm still cautious about *investing* using Robinhood, but now that they've opened up their platform to Quantopian, Openfolio, etc, it's beginning to seem like an attractive brokerage for (systematic) trading.

My devil's advocate encourages you to go for it. Nothing quite like learning from the mistakes of others.

Just kidding ;)

There are several features of the RobinHood app that make it simultaneously useful and detrimental to the average investor.

Pros

• Intuitive interface, easy setup, no commission fees. The UI is the best I've seen in awhile.
• An investor following sound investing principles will save about ~$100-200 per year on trades.

Cons

• Low barrier to entry to the stock market encourages fools that don't know what they're doing to jump in deep, deep water. The minimum age to download the app is 4+, for Chrissakes - think of how many 14 year olds who think they are the next George Soros and dump all their parents' savings into APPL. The media has portrayed stock trading like this:

or this

or this

Stock trading isn't that easy.

• The way Robinhood makes money is interest fees on cash balances and interest from margin lending. Interest fees on cash balances encourage a portfolio allocation weighted in stocks (which is what Robinhood supports at the moment), because investors don't get as much return on cash. Over-weighting your portfolio in one equity class is generally not very sound.
• I think it is a travesty Robinhood is exposing margin lending to average investors. In the wise words of Kendrick Lamar, borrowing is for suckers.
• Reducing the fees on trading is more economically optimal... or is it? The answer isn't clear but I can imagine that if there is a paradigm shift from centralized brokerages to every Tom Dick and Harry buying in and out of the stock market several times a day, the markets might behave more irrationally. I don't think this will happen, but depending on how large of a market cap Robinhood intends to capture, it's really hard to say what will happen. Edit: In light of recent events (i.e. the Chinese stock market crash of 2015), it's become quite apparent that a market with 85% retail investors by composition has higher volatility. Too many retail investors a la Robinhood might not be a good idea either.
• The user interface tracks market movements in real-time. Pretty cool, but an investor should avoid being swayed by short-term market movements.

Robinhood doesn't smell like a scam to me, but the road to hell is paved with good intentions (just look at how many a Bitcoin exchange / mining cooperative turned out).

I believe Robinhood is behaving irresponsibly as a brokerage, with regards to the best interests of investors. By dangling free trades in front of the investor and offering margin lending (good god), the company is encouraging investors to trade more frequently, which is a pretty bad idea by most long-term investment principles.

If you are an investor, it is prudent to avoid putting a lot of money into new ideas, especially ones that claim to be revolutionary. The maximum drawdown of operating with this sort of firm that is completely new to the game is 100%. Although they are insured for losses, I suspect the fretting is not worth the 1-2 hundred bucks you save on trades per year.

Instead, I encourage to go the boring but time-tested path of putting your money in a Vanguard mutual fund, and choosing a diversified basket of funds/ETFs. Read up some of the bland classics on investment and learn the big mistakes people made in the past (Burton Malkiel's A Random Walk Down Wall Street is good to steel your mind against temptation and hype). Only trade a few times a year, and buy things that you wouldn't mind owning for 10+ years.

However, it would be interesting to see how Robinhood turns out and what average returns people get from this somewhat-disruptive product. Personally, I intend to monitor this and see how it turns out for others.

Disclosure: my answer does not constitute legal financial advice, and I assume no responsibility for losses / gains as a result of people reading this post. Not for reproduction.