Big thread over on boards listing issues with the horizon box. I've just got it installed a week or so ago, and have had some issues. Not a big TV watcher so still testing it. Its a very slow box in general. So far its missed some recordings and cut one off short. Not good considering I've only had it a short time. The user interface is poorly designed. It also lags and then catches up with key presses.
They put delete everything off the box right under the delete option for a single recording. With the lag people are going to into that by accident, or not realise its for everything not just that series and delete all their recordings by accident. Truly awful interface decision there.
I only went for it because of the 4 channel recording (nothing on all week then everything on the same time and evening etc) and more HD channels. I'm totally convinced all the HD are worth it. Some of them are dire. I didn't have anything before so I'm not missing a better system like Sky, or Free to Air. If I had those I wouldn't switch to the horizon box. I think the old UPC box was better. In fact we had our parents cancel the horizon and go back to the old box and they are much happier.
I also got a seperate modem/router TC7200 and I find this a bit limiting as you can't use you're own wifi router with it, (easily) and the wifi range on the TC7200 isn't as good as my old €35 router.
On the plus side I'm enjoying the HD that is worth watching, and having 4 channel recording has already proved handy. Especially with the kids.