I use it even though it doesn't work perfectly with all of the mods.
Modman sometimes gives me problems with installing/uninstalling certain mods. It will sometimes install some parts of the mod in the wrong location. When I decide to uninstall the mod, it sometimes (in my experience) does not uninstall the mod completely leaving some bits and pieces.
It could be a problem with Modman itself or the improper steps taken by the creator of the mod making it Modman compatible.
If I want to try a mod. I would just back up the original folders where the mod will be installed so that if something goes wrong I know I can go back to original state.
Even with these shortcomings I still use it to identify the folders where the mod will be installed specifically. I voted 'Yes' ;)