I just changed my fuel filter, the connections to which are rubber fuel line fitted over metal pipes with bulging ends -- a bit like a barb.
(There's a photo at http://i.stack.imgur.com/oH0Ns.jpg if you like.)
The hoses were an absolute beast to get off; I ended up using a pair of pliers to help me twist them enough to get started, which naturally made me worry about damaging them.
I have no idea when the filter was last changed; I assume that the hoses did, and are going to again, "settle" somewhat onto the connection. I'd like to put some kind of lubrication on the metal so that it's not quite such a fight at the next change.
The recommendation I've seen that makes the most sense to me is Vaseline -- normally, of course, one shouldn't put petroleum lube on rubber, but this is fuel line.
Fuel or motor oil, along with silicone and dish soap have also come up. I want the lube to be persistent, though -- I can't imagine that the slipperiness of gasoline will still be there in another 30 months. Dish soap likewise tends to dry to a sticky film. I've heard rumors of silicone damaging catalytic converters when its makes it way into exhaust. Motor oil on my fuel lines sounds like a recipe for fouled plugs and injectors -- but maybe Vaseline would be too?
Should I pop the lines back off and apply a little jelly, or should I just leave it be and resign myself to the struggle next time?