I've made a complete migration from Drupal 5 to Drupal 6 with my website. You'll see a lot of changes on here and overall I think it's a fantastic change and will last a lot longer in the end.
The primary motivation for me to do this was that I didn't like how dependent it was on contributed modules. When the beta versions of Drupal 6 came out, I wanted to make the upgrade, but couldn't since I was using a hilarious amount of contributed modules. These contributed modules, of course, had not made the update to 6. Now I'm just using Drupal core, which will make it much easier to update to future versions of Drupal as contributions will always be behind.
The majority of the features in Drupal 6 are in the administration and its API, so you guys won't really see anything new by visiting this site. The things you will notice, however, are new looks for the articles and projects sections, the gallery now aggregates from Flickr, and the links page aggregates from Delicious. As more contributed modules get ported to Drupal 6, more and more things will appear. I'm really liking this release so far.