I can think of a number of disadvantages, but before I list them I think it's important to point out what the baseline is. In many organisations the knowledge-sharing environment is badly dysfunctional at the moment. A large organisation in which almost every written communication is by email has so little ability to exploit the knowledge base that is in its employees' heads that almost any alternative approach that increases the ability to do so is worthwhile. So it's not sensible to be too critical of whatever alternative is suggested.
That said, I think the main weaknesses of the approach I outlined in my previous post are these:
- We're introducing more places to look for and/or place information. A lot of people find it hard to keep up with email and the intranet and maybe something else like Sharepoint. They aren't going to thank you for suggesting they should use more software in their day-to-day activities, perhaps
- The niceties of what you can say and to whom online are managed in a very fine-grained way on email at the moment - even forwarding tends to be done judiciously by experienced users (and that's most employees). The approach on a blog or wiki would need to be different. The change of habit could be a barrier to use
- RSS (and aggregators) and tag clouds might seem intuitive to a geek, but may be less so to the average user. Again, we are talking about a small extra effort being enough to put many people off switching from what they know and (sort of) love now.