I think providing a gigabyte per user is simply phenomenal. The google guys do come up with good stuff! I can't imagine the magnitude of storage that will be available say 10 years from now!
However, I think the privacy is going to be a major concern. It states that it'll come up with ads based on the content of the email messages. I'm sure people are going to object to that. While most of us wouldn't have stuff we'd be VERY secret about, the idea that someone (even if it's a computer) will be scanning our email content on a regular basis wouldn't give a particularly secure feeling to a lot of people. But I guess it's not such a big deal after all.
They say that we'll be able to search through any email we've EVER sent / received. Does this mean that we'll not be able to PERMANENTLY delete any message? It might show the message to be deleted but will it be stored on the google servers?
All in all, it would be fair to say that I can't wait to register for it! :-)