A lot of times, organisations have custom attributes in their Active Directory user profile. However, by default the user profile sync happening between Sharepoint and AD does not include these custom properties, such as EmployeeID. Hence, we can’t retrieve these properties in Infopath.
Typically, users that are already added to a site collection are displayed in the People Picker. This prevents anyone from using the People Picker to browse a different user directory. However, in a hosting scenario, you do not want end users to be able to search users from Active Directory; you only want the end users be able to search users that are already in the site collection.
User profile management can be a nightmare in Sharepoint 2010 when some users reporting their job title or email address appearing incorrectly in People Picker search tool. This seems to vary if they search on Last name or First name. Depending on the situation, People Picker returns either the correct, up to date profile information or the out of date.