The original plan for Project Canvas nee YouView was that it would be available at the same time as the switchover really got going late November 2009 or slightly more realistically (LOL) in Spring 2010 when Freeview HD products became available.
Instead they may launch it before the end of the switchover if they are lucky.
In terms of likely commercial success for the platform it is pretty limited. The set top box/PVR market is tiny compared with the TV market and the retail position of such products is almost non existent with virtually no products connected to TVs and those that are are almost never demonstrated.
Youview has two potential opportunities. The first is if a slimmed down (disk free) profile could be developed and included in a major brand's TVs (Samsung, LG, Sony, Panasonic) which I don't think is tremendously likely because it is so UK specific and they all have their own UI's and platforms already.
The second opportunity is the amount of support the telcos may give it as a managed network set top box. BT Vision has about 700,000 subscribers but I wouldn't expect them to make the massive investment to transition all of them to YouView devices but it will be interesting to see what business model they proceed with. TalkTalk doesn't yet have any TV subscribers I believe. These telcos may believe that their current internet users will flock to YouView devices but I don't see it being a strong enough pull to draw people in without good offers.
My expectation is that Youview will never catch up with the reach of internet platforms offered by Samsung or Sony TV even in the UK not to mention the XBox and PS3 which will lead to it not being the clear target for content so I don't think it will sustain a substantial content lead.
You may notice that I don't discuss how well designed/advanced/clever it is. That is because I don't think it matters even if it is brilliant, the commercial opportunity really isn't there.