What are some common criticisms of Sharepoint as a knowledge sharing tool?

In practice SharePoint tends to encourage information “stovepiping” and the accumulation of information in non-permeable form (i.e. big dumb files).

Comparing SharePoint to, say, MediaWiki, SharePoint is much easier for most users to approach. There’s no markup language to learn to start using it, no implied way of organizing information. However because SharePoint relies on so many of the same metaphors as single-user desktop computing (e.g. file folders) it doesn’t encourage users to approach it any differently as a knowledge repository.

As an enterprise tool it’s designed to be feature rich to accommodate the diverse needs of a large organization, and this includes permission controls. The ability to control access to certain types of information is necessary for specific business groups (HR) however in practice permission controls are over adopted by users who want to protect their little pockets of knowledge. True, this might look better than this information never being “shared” anywhere, but it does nothing for organizational knowledge.

The second criticism is that most users approach SharePoint first and foremost as a central, slick-looking file repository. The team behind SharePoint probably had and has much greater ambitions than this, but the average user when presented with the option to continue doing things the same way will, and that way is uploading files. Knowledge in centrally available files is better than none, but not by much. For an organization it’s of magnitudes greater value if knowledge products are in an immediately readable, searchable, and malleable format. The small up front effort to write or even paste information into a wiki page yields dividends when other people in the organization are required to open bloated PowerPoint decks looking for the answer.

As a bonus, the intentional editing required of a wiki usually yields superior organization and quality of content.

This is based on some observations of SharePoint in the wild (prior to the latest version), not based on technological capabilities or the intent behind certain product features. I do not think the intended design for how an application will be used is all that important if it is consistently used in a contrary manner. It’s also important to note that even some wiki products allow for permission controlling wiki pages and groups of wiki pages (e.g. Confluence).

Regarding the choice of MediaWiki for this comparison, I’ve watched non-technical users (the kind that only know MS Word, PowerPoint, and “Yahoo”) learn to use MediaWiki to collaborate on projects within and beyond the enterprise while flailing to do anything useful on SharePoint beyond upload files.