The biggest problem I've been having in the last few days is getting my Apple TV to see the home sharing on my iMac. And before you ask, yes, I had it all setup correctly on both my Apple TV and iMac.
The problem is that it would work - and would then stop working for no apparent reason!
When I got home tonight, I decided to do some diagnostic work on the network & router using my work laptop. I had a hunch that the problem was that there was no route between the devices (ie the router wasn't routing).
The tests that I did seemed to prove that.
I found that I couldn't ping any of the devices on the wireless lan - although I could ping devices on the ethernet ports. I tested each of the devices (the iMac and Apple TV) and found that they could access the internet - but just couldn't see each other.
What's annoying is that everything started working again by adjusting a property of the wireless network (eg I switched off the "Allow multicast from Broadband Network" option).
I've repeated the test by adjusting other properties (eg switching from automatic channel selection to manual selection).
This is extremely frustrating and seems to point towards the wireless stack in the Thomson router being flakey (as others have reported).
I'm thinking that swapping to a new wireless modem router is the best option - but it does frustrate me that I've been locked into another 12 months with Telecom in exchange for what now appears to be a completely rubbish piece of networking equipment 8-).