What is the best strategy for Multi-DB

Hi

I have been advised to not worry about multi db for the time being as my wpmu network is in infancy. (30+ sites)

However, I can clearly see that the blogs are being created in approx 4 categories. (blog types will one day associate these blogs to a category)

In order to be forward thinking, should I start breaking up my databases to suit these 4 categories of blogs?

Or should I wait until I have a good 200 sites before acting on this?

Many thanks in advance,

Johnny