What Dries say in this article:
"The "sweet spot" for Drupal is larger sites rather than smaller ones. "I think when people think big websites, they usually think Drupal, and when they think small blogs or limited small websites in complexity then they think WordPress," Buytaert said.
"At Acquia we never compete with WordPress. We don't see them ever. I'm sure the smaller Drupal shops run into them, but in the enterprise we never run into WordPress."
"I think with small sites I'm not willing to give up on them but I think we just need to say we're more about big sites and less about small sites, but then the small sites are still very useful to get people into the community," Buytaert said."
I would have liked to know that before... I moved from Slashcode to Drupal years ago on the advice of a few. While I can appreciate how Drupal is flexible and powerful, now I understand that what I really needed, as a non-expert and for my small website, was just WordPress. But too late, won't do another painful migration anytime soon...
What annoys me most with Drupal: no straightforward way to update major versions (e.g. from 6.x to 7.x), especially since a lot of user-contributed modules doesn't exist in the new version or require a lot of work to do so. The admin interface is pretty bad. The user community is much much smaller than WordPress (thinking of mature/maintained user-contributed modules here). Etc.