What people typically do is setup nginx as a frontend proxy to serve the static content and let apache handle the php. I know SD has done this as we've talked about this pretty extensively. I believe he did this using a cPanel plugin. I didn't get around to pulling the trigger on this due to a lack of time, and the fact I got sidetracked trying to implement Varnish. What I discovered is varnish is a pain in the ass, and quite surprisingly isn't any faster then nginx in some of the testing I've seen. It's still not clear to me how .htaccess files are handled in a frontend proxy setup, but I don't think any changes need to be made. I'm actually interested in finally doing this so maybe we can work through this together.
There is a lot of info about running nginx on the IPB community website. There is a ton of info out there though about setup a frontend proxy so you shouldn't have any problems.
SD also has written a mod for switching over the search functionality to using Solr.
Won't you take me to Funkytown?