Use Case: To allow anonymous user to do People Search. Why would you consider this use case? Well you are reading this so I am sure you have one. One of use case is that for two companies to have ability to provide people search.
When you enable anonymous access and do people search you will see prompt for Authentication. Cause of the prompt is Search Core Results Web Part. There are enough discussions on building custom people search and how to do it. Another option is to login Anonymous user under Guest Identity.
Here are the steps:
1. Setup FBA (Unfortunately it only works for FBA Zone) - you can refer to Dan's blog here.
2. Create a dummy user and change global.asax file as per Reza's blog here.
Logging in as Guest Account also has other added advantages for WCM solution in which anonymous user access does not work.
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