Picking number of databases for a fresh install

Read through all the threads in this forum and what I could find on the Web about different views on number of databases you should set with initially.

Realize it depends on situation and lots of factors but would the following be a really rough ball park guide?

If more than a few hundred blogs, consider going to 16 databases?

If more than 50,000, 256 databases?

If more than 100,000, then 4096 databases?

Just wondering what is the downside of starting with 4096 databases right off the bat for a site that could potentially end up with really high number of blogs and traffic or for a smaller potential site, still starting with 256 even if probably not needed.

Is it just more of a pain to manage or does it actually slow things down if there are too many databases and they aren’t necessary for number of blogs? The threads said it was difficult going from 16 to 256 and saw Dr. Mike say he just sets at 256 for all of them… any downside to this approach?

Trying to get sense of trade-off between extra work at the beginning setting up with more databases compared to the extra cost and hassle down the road if you wait until traffic grows more to start increasing number of databases.

Thanks.

Cyri