Hi Spencer,
I am a huge proponent of WordPress, and it is (in my opinion) the best SEO CMS available. For starters there are excellent Plugins such as HeadSpace2, and the All-In-One-SEO-Pack, which allow you to manage title tags, meta data, redirects, ect.
WordPress also has other excellent plugins for SEO including SEO Friendly Images, and SEO Tag Cloud. Also, WordPress has awesome sharing widgets such as Sexy Bookmarks.
So in conculsion any design limitations are far outweighed by the overwhelming amount of SEO and sharing widgets available. The real limitations for WordPress is not in the design department it is in the Intranet department. However, if having an intranet is not important then I would say WordPress all the way.
C
