Sorry Vince, that wasn't very helpful was it? I go to the 'View unread posts' bit and there's nowt there, so I click on the 'View Active Topics' and there's loads with the 'New icon' next to 'em. I realise I''m a bugger for jumping on the forum on different machines but many of these are genuinely new posts/threads. It's been quite noticable the last few days...
It's not a big deal, I'm happy to use the Active Topics bit if it's something my end, i.e. cookies or some such.
Oh, and typically, it's working again now!