I opened outlook 2007 this morning, and all my custom calendar categories and colours are gone. When I check the categories all the custom names are gone also. I've checked my calendar on a few machines to ensure that it isn't something local.
So, basically, in my calendar I used to have 3 colours assigned to categories and EVERY appointment had a category assigned to it. Now not a single appointment is coloured OR categorised.
I also noticed at the same time, my smartphone that normally syncs over GPRS with our exchange server is no longer syncing calendar and contacts (email is syncing fine).
I'm not sure if these are related but it seems likely.