To paraphrase Joe Lubin's on our forums (https://forum.ethereum.org)

We are not conducting an IPO. We are not selling shares in anything. Ether (ETH), the product we are selling, has no voting or any other kind of rights and does not entitle anyone to dividends or any sort of future gains.

Ether is a necessary element -- a fuel -- for operating the computational platform we are building. Without the requirement of payment of ether for every computational step and storage operation of the system, we'd hit the halting problem (http://en.wikipedia.org/wiki/Halting_problem): infinite loops or excessive storage demands could bog down the system and effectively destroy it.

People can download the software platform and run it on their computers and it will do certain basic things like perhaps showing them a catalog of available apps. If they want more functionality, like running a DApp or uploading and testing DApps that they have written, they will have to feed fuel into the machine.

Under Swiss law, where Ethereum Switzerland GmbH is based, the product we are selling is classified as a software product. And we are conducting a pre-sale for this product since we are not yet able to manufacture it.

People who are interested in acquiring ether to build and distribute DApps, or to pay for their usage can do so in the pre-sale, for BTC. These sales will help us fund the continued construction of the software platform that requires ETH, tentatively due for release in Q4.