Have had this in the "drafts" section since a while.....
Even though I have a 46" LCD TV, I am not too keen on paying my cable distributor an exorbitant amount of money each month to receive HD, keep a DVR and then watch the few TV shows of interest on my own time which is generally between 12:30am and 2:30am in the night. So, the most convenient way for me is to watch them on my laptop which has a decent 15.4" screen and the Toshiba TruBrite (c) technology.
Obviously the convenience of not being tied to the television schedule helps, but even the commercials are fewer for the online versions and you can run some scripts while watching without having to look up from your screen!
As a simple desire, The Daily Show is available the next day in flash which plays in Firefox, so thats a start.
As for network stations, here is the breakup for the big three stations (non-cable)
ABC - This has probably the best quality HD programming which looks great on a large LCD if you try it. The catch is however, that even though it works great it Firefox, it needs Windows. I haven't checked recently, but I doubt there is a Ubuntu port for that flash player/codec?
NBC - They have some of their best shows (which is not many) available in flash and the player/interface is not bad. Plays in Firefox.
Fox - Their flash player also needs an installer for Windows, but probably runs in Firefox. Can't get it to play in Ubuntu...than again, I don't want to spend any effort figuring this out to be able to watch How I Met Your Mother!
I had read an article in Business Week a few months ago talking about this thing in particular; Online TV (as opposed to IPTV, which is a little different). Its an interesting read, and things are constantly changing it seems and moving in the right direction.....as far as the consumers are concerned.