Hal Richman wrote a short article in his blog about workplace learning, and is quoting the The Educational Development Center in Bosting about how people learn informally. No surprises here for all of those who work actively with communities of practice (read: communities) but it's good to have some figures again to further substantiate it:

• Approximately 70% of the way employees learn their job is through informal learning;
• Employees acquire a large variety of skills informally, including many skills which cannot be acquired formally;
• Informal learning can be influenced by the organization or management; and identifying and implementing the factors which impact informal learning can greatly increase the quantity and quality of skills employees will acquire informally;
• The economic benefit of informal learning to firms is statistically significant.

I do not agree with Hal's precise distinction between the informal learning environment, where he includes communities of practice (specifcially designed?) and the accidental learning in peer-to-peer communication. I see the communities of practice as way to encourage informal learning, but think that they need not be designed, supported, encouraged or even endorsed by any organization to fit its purpose. And the peer-to-peer communication and conversation I reckon is an exponent of the community of practice itself.. it only becomes accidental learning (I do not like this term, but recognize its use is widespread) when it comes to "supervision", "exit/entrance interviews" and "peer assist" (BP). Accidental because they are planned, designed and formalized. Yet, these types of learning could be part of the crossover learning between these two learning types, for instance in the backchannel of the communities.