No public stats I can personally provide. But I have seen it vary wildly depending on the type of service. Businesses are generally slower to adopt a new service/tool, and once they are locked in can be apprehensive for change. Consumers can change on a whim if something better comes along.

Here are some interesting stats I found for Evernote: http://techcrunch.com/2010/05/28/video-evernote-ceo-phil-lib...

Evernote has been pretty open in their stats over the course of their existence.