For me it depends.

When travelling home airline I dont bother (unless I am using an easy-check machine). They can retrieve my booking easily from name off passport. For other airlines, if travelling on eticket I usually provide the card. IMHO less hassle than a printed itin. If travelling on a paper ticket I wont bother, unless I think there's a chance my FFP# isnt entered (or I've changed my mind which one to credit to since booking).

Sometimes card comes in handy if there's someone guarding which line you can use to check-in.