KRunner doesn't seem to offer the same functionality it had in 9.04.

For example it will no longer do unit conversions or find contacts and I cannot get the spell checker to work (I've tried configuring it but this has made no difference).

Any ideas?

Open krunner, on the far left should be a wrench icon. Click that. You should see a list of available plugins. You should be able to enable or disable plugins there by checking or unchecking the box on the left side. If the plugins you want are no longer present that is because you either didn't install them (check your package manager) or because the kubuntu team didn't package them at all.

Thanks, it looks like the Kubuntu team left them out as I have never needed to install them before.

I've just had a quick look in my package manager and have found plasma-runners-addons which says "If you use krunner a lot, you will probably like this package." Sounds like this is what I want!

Yup, that did the trick.