The only reason to have a destination URL is if that URL is going to get into the public consciousness. I do not know how many companies have created microsites in the past year, but I can tell you that those that have penetrated my consciousness can be counted on one hand.

I know there are exceptions, but most of those exceptions, like a "downloadable piece of software" where you want to drive people directly to the download page, usually just require a single landing page, not a microsite.

Simplicity rules. Look, the technologies exist -- Pointroll, Eyeblaster, etc. -- that allow you to integrate the microsite concept into an actual ad. There are several advantages to that approach. The development time is much shorter. It is much more cost efficient. There are no associated hosting fees or maintenance fees. You get a much bigger bang for your buck with your consumer, and when the program is over, you just pull the ad. You are left with no orphans, whereas microsites take too long to develop, are usually managed by committee, have a relatively short lifespan, cost too much, use up agency resources, use up client resources, use up money and become orphans almost the day they launch.

Look -- do what you want, waste your money, but if you are going to do it, do it fast and cheap and don't try to bolt on every feature. Streamline your construction and develop a microsite strategy. As long as you look at them on a project basis, all you are doing is making your agency rich.