Membership in caml

<Or>
  <Membership Type="CurrentUserGroups">
    <FieldRef Name="AssignedTo"/>
  </Membership>
  <Eq>
    <FieldRef Name="AssignedTo"></FieldRef>
    <Value Type="Integer">
      <UserID/>
    </Value>
  </Eq>
</Or>

查询包含User或者等于User的数据

http://msdn.microsoft.com/en-us/library/aa544234.aspx