This preview isn't intended to be widely used by the general public, but if you're reading this blog you're probably technical enough to try it. Over the next few weeks I'll post about some of the features I've been working on. Posts on the IE blog will be intended for a wider audience, whereas any I personally make here will be more informal and technical.
Last but not least, for general questions and feedback you will get the best response by using the newsgroup for IE7 and file bugs using the instructions provided in this IE blog post. (Unfortunately I'm unable to answer everybody's questions when they email me directly.)