As a programmer with absolutely no design skills, and markup skills that haven't quite made it into the web 2.0 era, I always collaborate with others when building a new site from scratch, or when embarking on a redesign or any substantial UI changes. Usually I act as the themer, transforming finished markup into a set of templates.

Getting Drupal friendly markup from the start makes the task of theming much, much easier.

Drupal 5 scales really well

This surprised me. Having run into many of the common Drupal scalability problems on smaller sites with shared hosting, I expected much worse. In the process of migrating National Novel Writing Month to Drupal 5, I discovered that there are number of contrib modules, patches, hacks, and techniques that can be applied to allow Drupal 5 to scale to handle a medium-traffic, high authenticated/anonymous ratio, web site like ours, as long as you can live without modules that use the node_access table.