multi server site

i know its easy enough to put the database on a separate box and use caching tricks to get more mileage from my server. What i am looking for is information about how people are using multiple web server boxes all pointing to a single data source box. It can be cheaper to use multiple smaller instances at rackspace or amazon. I am guessing you designate one as the upload/write to database box. anyhow just looking for information in this area from people who are already doing it.