Major version changes of software are always scary, but according to http://www.drupal7releaseparty.org/, at least 234 people worldwide are excited enough to throw a party for Drupal 7's release, which is tomorrow. Drupal 7 has been in development for over two years, and is the product of over 1000 different contributors.
I've created a few sandbox sites with Drupal 7, and I'm excited. The open-source content management system has seen some significant improvements in areas where it seemed to be lacking. The user interface has been streamlined (particularly for administrative tasks), thanks in part to a sleek new D7 custom base theme. Site configuration now takes place on an overlay, without leaving the page. Under the hood, a lot of "optional" modules have been made a part of the core — things that are part of our default buildout of a D6 site will no longer require separate maintenance (which has the effect of reducing my update workload).
Professionally, we'll be assessing the strengths and weaknesses of this new version over the next few months. Personally, I'll be updating my own site as soon as I find time!