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SharePoint offers a set of collaboration tools. Social tools of all kinds like telephones, televisions, and trucks support certain kinds of social activities. What SharePoint really does is support kinds of social working, and to really understand SharePoint is not the technology as much as the social uses made by web pages.
In my experience the most popular SharePoint feature is the team site. A team site allows a set of members to share documents, comments, to make list items and track tasks. It includes the ability to make calendar items.
Over the past 5 years I have seen this tool more than any other used by businesses. Business is generally about project work which is what Information workers usually do.
Team sites not only support small project team working, they also avoid some of the dangers of other web 2.0 tools. Unlike Wikis its unlikely that a small team will get side tracked with arguing about how the SharePoint site should be created, mainatined or governed, or who has control over it. Unlike blogs there is little chance that producers will concentrate on status and kudoos over doing some work. Discussions among team members who work together are not likely to contain flames. Team sites are generally safe ways for busiensses to make clear use of Web 2.0 featues.
But there are also negatives to team sites. These negatives are the negatives of teams. Remember its not the tool but the kind of group that the tool is used by. Team sites are used by teams and thus the problems of teams are the problems of team sites.
Teams can develop loyalty with established members wanting to work with each other and not allowing new members to join. Team sites can produces an internet of unconnect little kingdoms that don't work together.
Teams will inherit work without a clear understanding of the history of it. SharePoint reflects these problems. Team sites are generally be created without any information about the pre-history of the project. Work is repeated. Clients get billed again and again for the same work until they have enough. It becomes hard to join up small teams in to enterprises. You get a few gurus with some people around them over a company able to form to meet new needs.
When using a Team Site or planning Team Sites you should think about how to prevent a team from becoming a clique.
How can you connect teams to a company wide vision?
I think RSS feeds that come from company wide blogs or other information feeds to put the big picture there. Using an tool like Quest's web parts will enable the business to collect data from teams. Also trying to keep standards can promote shared working standards.
I would also suggest you talk to your users and get them involved in the process of making teams that work with the company. SharePoint is only a space to do social work, you still need to work with the people.