A great summary of the capabilities of Sharepoint and a must read on it's weaknesses and limitations:
SharePoint architecture, which is not inherently collaborative, is based on a much older model of “publish and subscribe.” It is very top-down and hierarchy supportive, more like a Web 1.0 (or pre-Web) application than today’s Web 2.0 social applications. SharePoint is really a Web 1.0 tool more focused on content than people.
SharePoint’s architecture comes from a time of “non-transparency” where security was more important than sharing. Each site can be its own mini-silo and can’t see any others ...
Funny, that a product carrying the share in it's name is more focused on hide in silos. We are going (or we are already) in the Social Business age, where we move from a file-paradigm to a share-paradigm. First this is a cultural issue, but secondly it is a tool-one to: Sharepoint is not a platform for Social Business, whatever Marketing is claiming it to be.
SharePoint still only runs on Windows, and it was not originally built as a collaboration tool, but Microsoft keeps bolting on collaborative functions and calling it a collaborative tool. As I said, the marketing is pretty convincing — but you make your own decision.