don't get too greedy

Can you blame them?
Speculators and investors: No.
Developers: Absolutely.
So let’s think for a minute and think what determines the price? Supply + demand. Pretty straightforward.
Supply: the tokens that are available on the market, right? But with every ICO there are more tokens that are being “locked up”. Obviously the projects will liquidate some, to get fiat to pay for development of their project, but they also see the rising price of Ethereum. So at that point greed takes over and they think, totally understandable, “We should probably just cash out what we really need and keep the rest in ETH, that’s only going up anyway it seems.”
And obviously there are new coins being mined, but if you look at the amount of ETH these ICOs raise, at this point, it’s just a drop in a bucket.
Demand: You have the normal investors (who are already very late to the game at this point… as usual), but the buy pressure that these ICOs are creating is crazy and scary. Take TenX for example, it’s an upcoming ICO at the end of the month. The cap is 200,000 ETH (at current ETH price of $370) that’s $74,000,000 for a startup. Here’s the best part: it’s only 51% of the tokens. Effectively giving it an instant $150 million valuation (if it sells out, which it probably will).
Another example is Bancor, a friend of mine runs a trading group, he collected 1,100+ BTC to put into Bancor. This needs to be converted into ETH before the sale starts. These are decent size players, but not even the big whales who participate in these ICOs.