Just got this question in the Ask-The-Experts stand in Tech.ED europe. If I use the people picker like I showed in a previous article, how can I specify if the users can pick a user or a security group or a distribution list?
Well, the answer was in the SDK - there is a property "SelectionSet" that accepts a comma-delimited list of strings that say what can be picked.
For example, "User,DL,SecGroup" will allow users to pick user accounts, distribution lists and security groups. Choosing just "User" will allow only people accounts. The sharepoint people picker ususaly sets "User,SecGroup,SPGroup" or "User,SecGroup" or just "User"