As any product gains in popularity, especially if it's seen as dominant, you tend to see more and more news about alternatives that inevitably get dubbed "killers." The news media and the product's competitors are continually trying to best the dominant solution and predict a product's demise. We can see this clearly with the iPhone and, as Seth Gottlieb pointed out, "who isn't working on a SharePoint killer?" But in many cases, these "killers" are only hopefuls with virtually no evidence they could harm a fly.
I don't want to suggest that there aren't viable competitors to SharePoint. Far from it. There are a number of very good tools that have similar functionality. However, as a consumer you need to do your homework and ensure that you're choosing the tool for the right reason: it meets your business requirements. This is true whether it's SharePoint or Alfresco (which has also been positioned as a "SharePoint killer").
To illustrate my point, take Hyperoffice. Their Google ad (run on an article about SharePoint) reads "Why Pay for SharePoint... Affordable SharePoint alternative... " Hyperoffice does provide document sharing, e-mail integration, calendaring (both personal and group), as well as task management and forums (among a number of other features). I especially liked their task management functionality, since it included the concept of a project. Hyperoffice also provides the ability to view their repository through Windows Explorer or the Mac finder, which provides basic Office integration (though not anywhere near SharePoint's integration).
But with all of these features, it is really a "killer" or a true alternative? No. Hyperoffice, in particular, was careful to use the word "alternative" instead of killer. However, their idea of an alternative only addresses Windows SharePoint Services (WSS) functionality. Some features were stronger than WSS and some weaker, but their pitch ended up being about price. The problem? WSS does not have a license fee. Further, their tool does nothing for organizations that need the more robust features of Microsoft Office SharePoint Server (MOSS). While they give you the facilities to share lots of different kinds of information, this approach is a far cry from a true enterprise intranet -- even for small and medium organizations.
SharePoint's success is in fact partially attributable to the fact that it covers such a broad array of functionality and can be "bought" in many difference configurations. Is every function best-in-class? No. However, Hyperoffice (and firms like them) make the same mistake that many organizations make with SharePoint: they provide a bevy of features and hope business users will figure out what to do with them; it's another "build it and they will come" fallacy.
Readers of our SharePoint Report 2009 will know that SharePoint is more than just the collaborative features found in WSS. In our research, we turn a critical eye to the value in the MOSS additions and the ecosystem that surrounds SharePoint. However, you should be suspicious of vendors who are marketing themselves as an alternative or a "killer" (especially those who use the "price" argument). These alternatives may have equivalent features or may be superior for specific use cases, but you still need to evaluate them objectively. In many cases, I suspect you'll find the "killer" isn't anything of the sort.