Came across an annoying but simple to fix issue recently, Users on CRM 2011 with CBA/IFD were being asked to login again during the day for no apparent reason. The timeout on ADFS was 12 hours so it should get them through the day.
After a lot of digging I found that an IE setting was causing it, in the Advanced Tab theirs an option called [Empty Temporary Internet Files folder when browser is closed].
So the scenario was, a user had outlook open, then opened CRM in IE, or a Report etc.. Then closed that window which deleted the CRM and ADFS Cookies. The CRM Outlook client then proceeded to ask for their login credentials again.
By un-ticking this option it wouldn't ask.