In his keynote at DrupalCon Boston on March 5 Brian Aker discussed the latest approaches to six problems related to scaling up MySQL:

When Easter approaches, my family has a strange tradition of

It's sometimes really cool to be able to share some of the tables between multiple Drupal sites. Just think your users have the same logins for example.

There is a lot of functionality crammed into Drupal. This can be a good and bad thing.  One of the key benefits is that its components are well maintained.