Well, I’d say no, but it depends on your definition of what web content management is (assuming you even believe it exists). WordPress is weak on workflow and approval. There’s no in-context editing. The metadata options are limited. Extensibility is somewhat idiosyncratic, to say the least. And so forth.
At the same time, if you follow the #cms hashtag on Twitter, you’ll see a steady trickle of links with titles like “10 best websites using WordPress as CMS”. And of course, it can be a very good solution in many scenarios where a more CMSish CMS would also be an option to consider. There are three huge pluses: instant-on deployment of new sites, integrated near-realtime analytics (albeit very limited), and good usability (well, compared with other services in this space: MovableType’s recent imitation-is-the-best-form-of-flattery redesign is an indicator of that).
There’s also the question of whether it might evolve into something more like a real CMS over time. I’m doubtful: the interface and (no doubt data model) betray its strong focus on blogging. And as far as I can see, this is a route that Automattic anyway have no real interest in; or if they have, they’re been slow to reveal their hand.
Rather, they’re leaving it to third parties. I’ve mentioned Pagely before. Tierra Innovation’s WordPress CMS Toolkit is another example of how some companies are taking up the gauntlet here. Their toolkit provides a set of plugins that can be used to extend WordPress in the direction of CMS. It looks pretty early stage to me, and the additional functionality in the plugins is pretty weak—still, will be interesting to see how this evolves.