Folder Size Column on Explorer on Windows Vista/Seven

"I can foresee any major issues should you decide to build a plugin to do this, apart from the possible 32Bit/64Bit issue. This means making sure it will work on both. There is no-one I am aware of working on a solution like this.

I would recommend that you consider making it an optional thing however. I will however admit I have always used Total Commander for my disk management needs and it allows you to press spacebar over a folder, which will then calculate the disk space."