Help needed! Blog serves old version to first time users

I’ve recently set up a site for a friend, and added a WordPress blog later on (http://www.tourthrufrance.com/blog/) – I first installed it about a month ago. Friend has shown the site to a few people, and has started getting reports back that people viewing the blog see it as it was when it was first installed (ie with the Twenty Ten theme and no posts etc). However he and I both get the current version, with custom theme and content where it should be.

In short, I’m stumped. I’ve checked the back end and the theme’s still in place and it’s set up as the one the blog is using. I’ve not added any caching plug-ins, does WordPress come with caching software built in?