When I play the game, I spend a good portion of my time with the FMB. The ability to create your own custom missions and campaigns has always been a big appeal for me, both in Il-2 and in other games where level editors are open to the community.
I spent an unhealthy amount of time with the original FMB, as well as the creating missions for LOMAC and Crysis too.
I've forced myself to stop, because it just takes too much energy out of me.
For example, I spent four months, day in day out, for up to ten hours a day creating a single mission for Crysis.
Never again.
But I have as much fun building missions as flying...although I fear the scripting will be something I won't delve into much, which is a pity because that is where the true power of this FMB lies.