How long is the program running that the microsite is based on? If it's less than a year, don't do it. Worse, I see programs that are only really active for weeks or a month, while agencies spent four months building the microsite.

From almost the moment a microsite launches, it is dying, unless it's one of those rare sites that gets viral traction. Even then, that site will never be an ongoing destination. It will reach its buzz factor, get forwarded by everyone, have a huge spike, everyone will be talking about it, and then, like Oliver asking for another bowl of porridge, it will beg for life support. Microsites are orphans. The URLs are orphans. You have to keep feeding them, housing them and clothing them, even though no one really wants them anymore. How long do you have to keep that URL active? And what is the post-consumer experience if you don't?

If you are not ready to have a kid, care for it and nurture it until it is able to live on its own, then don't give birth.