It depends on what you mean by "Enterprise." It's a horrible choice if you're building a supply chain management tool, for example.
But if you mean "extremely high traffic sites" or "Sites with complex approval workflows before content goes live" or "sites that we can scale horizontally", then I'd say yes. There are quite a few very large scale Drupal deployments out there, from SonyBMG's suite of artist web sites to newspapers and magazines.
