I go to my MTB the other day. It has Avid Ultimate disc brakes. I squeeze the levers, they offer little resistance, go right to the handlebars, so that doesn't feel right. But the brakes are working. Then after a couple of minutes, they feel more normal. Noticed that on today's ride too, the brakes seemed odd the first couple of minutes, quickly returned to normal.
I describe this to my LBS, the instant response is 'air in the hydraulics, you have to bleed the air out of the system'. I ask him if this is tricky, he says 'a little', which essentially means that for me it would be like building a fusion reactor out of balsa wood, I'll bring it to them. He says that while the brakes work OK now, this condition does worsen with time.