Check your Plone site's cachefu setup: small improvements can help a lot. I assume you've got a basic cachefu setup pat down already, which only means adding your few custom content types to the "content" or "container" rules and saying you've got squid (and/or apache) in front. You get good results with that: this blog entry helps you pinpoint some extra improvements.
First the one and only indispensable tool: firefox' Livehttpheaders extension. Livehttpheaders shows you the raw http requests that your browser sends out. And it shows you the requests that comes back: are the caching headers that you would expect really there?
If I only have one screen, I normally open livehttpheaders in firefox' sidebar. Some problems are quicker to spot that way than by switching back and forth between windows. Disadvantage: horizontal scrolling if you want to look at details. The jackpot: dual screens. One for the website, one for livehttpheaders.
Now get cracking. Pick two or three typical pages.
There you have it. A couple of hints to help you get started with basic CacheFu tweaking. You can get a lot of mileage out of it, without having to write custom rules or header sets. Though that is fun and satisfying, too.
My name is Reinout van Rees and I work a lot with Python (programming language) and Django (website framework). I live in The Netherlands and I'm happily married to Annie van Rees-Kooiman.
Most of my website content is in my weblog. You can keep up to date by subscribing to the automatic feeds (for instance with Google reader):