The first thing Tahoe does is classify "organic" content. Organic is Microsoft's poseur word for documents created within a company.
Tahoe then adds versioning, including check-in, check-out features and simplified workflow properties. And Tahoe, at least currently, has interfaces for a variety of data sources, including a Lotus Notes adapter and one that can access Web pages.
Tahoe also includes tools to create Web portals. Put these elements together, and it's clear the technology is more than a document management system. It's a content management system, and it's going to eventually compete with Vignette's V5, Interwoven's TeamSite and Open Market's Future Tense products. More important, Sybase and Oracle have said privately that they're going to dive into this area as well. This means that the market for content management solutions might consolidate at a rapid pace.
I'm not sure why all these large companies getting into CMS means consolidation (yet), but it definitely means a crowded and (more) confusing space developing, as the definition of content management is stretched to fit what all these players are trying to do with it.
Taschek's main doubt about Tahoe is it's scalability. ("It's easy to use and manages content well. What's unknown is whether it can scale to handle hundreds of users concurrently.") The bigger concern should be usability and simplicity. Unlike CMS's for web publishing, where the number of people using the system is smaller and basically without a choice, getting something to work in the enterprise requires many more (potentially, less technically savvy) people to use it, even though it's not directly their job to do so. Any extra complexity can kill such a system from taking off. (I haven't checked out Tahoe yet, so I can't comment on it in this area. However, I was involved in an implementation of Site Server for a large Silicon Valley company. We ditched Site Server before we ever got it up because it was so convoluted and ended up building something from scratch -- which, in retrospect, was also more complex than it needed to be.)