Eh, it's always hard to get in and stay in shape, just like it's always hard to create and maintain any habit. Not all of us ever get "used" to a pattern of behavior, so there's always a fight to maintain anything resembling a pattern.
There is a bit of a motivational hump to get over, but once you are over it (forcing yourself to cycle half an hour for as week maybe?) then it doesn't seem like a problem at all.
There are quite a few cities in Belgium and the Netherlands that promote cycling though. :)
I would love to cycle to work in Brussels but I do not feel comfortable doing so.