You can't treat DRM incorporation like an afterthought. Thats like storing valuables worth millions in a $50 Walmart safe. Or plugging a $5K computer into a $5 power strip.
I've frequently disagreed with Derek on several points, but here he is correct. On one of my projects, we designed the license system as part of the product - it added a lot of extra time to our cycle, but it made a difference in the end - we almost never get calls about the license system messing up.
I think you will see a lot more of this 'Periodic Activation Check' based DRM anyway, so you'd better get used to it. If I had my way, the project I mentioned earlier would do that and kill all but the most current installation.