I maybe incorrect on this, but from some testing and a quick read of the code, it seems like the 6.x version of ESI doesn't over-ride theme('block', ...) requests, it just handles theme('blocks') / i.e. regions. Am I reading this correctly or am I missing something big? This seems like a problem for people that are using something like blockref to "manually" place blocks in a custom layout. It also seems like adding theme('block',...) support would be fairly trivial, but again I want to be sure I'm not missing something. Has anyone hit this before?