shopping for a scalable php framework

[eluser]edoornav[/eluser]
Thanks for all of the responses. I tried XCache and eAccelerator and got up to 75 rps (from 20). This is probably fast enough that it won't be the bottleneck in a large application.

Has anyone used this framework to build an application that had to scale to more than one application server or db server? What were your findings? Were there any parts of the framework that you couldn't afford to use? Thanks.

~rvr