On my TiVo box the On demand and Catch Up services are extremely slow. It will often take a few minutes for me to go through the process of getting to the on demand services and getting a programme started. Using my laptop is much much quicker (and a better picture quality, although I guess that's due to my television). Regularly as well after waiting some time, it simply says services not available.
I have seen on here many other people reporting the same thing. To be honest, the standard it is at currently makes it almost un usable - and so seems wrong that it should be considered part of our paid for services.