Can the state rein in McMansions?

Although slightly off the strict green building theme, an interesting intiative in Colorado caught my attention. http://www.time.com/time/nation/article/0,8599,1643151,00.html

In short, Boulder, Colorado wants to institute a McMansion tax. Homeowners who are willing to sign away the right to build larger homes will get a tax credit, and those who want to build bigger homes will have to purchase credits.

My questions are: 1) Is this an illegal restraint on the use of property, and 2) what will its ultimate benefit be?

There is little doubt in my mind that this McMansion tax will fail to withstand legal scrutiny. Since the main objections to McMansions are moral and aesthetic--as well as environmental and economic--I think it might be wiser (and more likely to withstand legal challenge) to tie a fee to ameliorate the impact the house will have on the community and the environment. For example, if there will be additional sewage draw, or roads, or fire protection needed, the inidividual homeowner will need to compensate the community.