On his blog, Michael Kimsal talks about a presentation he sat in on at this year's MySQL Conference given by Joe Stump from Digg.com:

One key thing he's repeating is using a service layer to access data asynchronously. His advice right now is to group data requests at the top of a user request, do them asynchronously, and then use the data in the rendering when it comes back.

They've published a PEAR package as an example of this asynchronous method that interfaces with Digg's API (http://services.digg.com). You can read more about the subject of his talk on the MySQL Conference website.