New readers seeing old stuff

I’ve recently set up a site for a friend, of course with a WordPress blog (http://www.tourthrufrance.com/blog/) – I first installed it about a month ago. Said friend has shown the site to a few people, and has started getting reports back that some of those 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?