well, a 1-2-2-2-2-1 would obviously leave huge holes and gaps in a team's defense. the center would be left vulnerable to attack. An effective formation will reflect the team that you are playing. for example: if you are playing against a team that is running a 3-4-3, you might need to run a flat 4 in the back depending on the effectivness of their forwards. It's all strategic.
Personally here at swansea, we usually run something of a 4-1-2-1-2, with a defensive mid/stopper placed directly in front of the defense, as well as an attacking mid right behind the forwards. However, we do occasionally use a 4-3-1-2, pushing the stopper up to more of a central mid role. Again, it all depends on who we are playing.