There are not many choices at this point to stream live online TV via boxes like Roku, and most other boxes will require a home media server like Tversity (supporting such software should be one of the top priorities for Roku, as it makes the use of the box much more universal). I have one, and even with Tversity, it is not perfect, it is still much more convenient to do it via laptop or home media PC with HDMI out. There are some players that can pick up at least some of the live streams, but you will always encounter something that it cannot handle. That said, I would wait for Google TV and see if they came up with a product that can deliver it. That would be your best bet. The reality is that there will always be websites that don't want you to stream their content, and it will be an endless battle of content producers against content consumers.
I think that eventually Roku will have to mature for more diverse content that allows them to be in competition with other companies. Yet, it would be an illusion to think that everything can be free. And in some cases, consumers would not mind to pay.
Honestly, instead of paying some $50 for 240 channels of cable TV, I would be fine with the 6 or 8 that I actually have time to watch once or twice a month - and if a box like Roku could come up with the ability to subscribe to each of these channels in HD for $2 or $3 a month, I would drop my cable without any hesitation. In addition, if it was able to stream live feeds of selected international channels in the USA, I would not mind paying $5 or more per channel of my choice, and I bet that many people would be happy to do that, too.
Yet for now this would require a major shift in thinking about television and its consumer on the side of the TV companies and content resellers, and I am pretty sure that they are not ready for this change yet.