The browser seems VERY promising. At least for me the page loading time is significantly shorter. I haven't tested the mail client too much, since I don't want to fragment my mails to two applications. Mozilla also features an IRC client, that currently lacks features, but it's supposed to be developed a fully functioned chat application. 0.7a is still such an early release that it still is too unstable to be used as a primary everyday browser.
Competition is always a positive thing.
Even if Mozilla does not make it to the status of main stream browser, it will at least kick Microsoft to the butt so that they will keep on improving their browser. We all deserve better browsers and Mozilla is a step to the right direction.