Michael Idinopulos blogs Why wiki's aren't like other IT:
First, wikis are not a scale play. A single business unit, a single team, even a single person can derive business value from using a wiki. Of course the network effects are exponentially greater at larger scale, but there's a lot of benefit even without the scale.
Second, wikis are not a standardization play. Traditional IT systems are all about trying to limit variation and get everyone to do things the same way (often for good reason). Wikis area all about morphing, molding, and adapting to the way people and groups want to work. So the grassroots appeal is not surprising.
Finally it's difficult to force someone to use a wiki. It's relatively easy to force compliance around a Purchasing, HR, or Finance system: simply mandate usage and take away the alternatives. But the alternative to wikis is email, and who's going to take that away? People will use wikis only if they want to, so the adoption has to come from front-line workers freely choosing the wiki over other alternatives equally available to them.
He goes on to note the economics of SaaS and Appliance models provide further differentiation. I'd note that his second and third points get at the difference for collaboration something you can't mandate from the top down. Andrew McAfee would chime in here pointing out the freeform difference of Enterprise 2.0, where the structure emerges as a byproduct of using the tool, rather than being defined in advance. Often and unfortunately by IT.
