Will Roku ever add a video preview pane with listings on the other side as an option? Is the reason for its non-existence due to Roku not being Java powered? The only way to play Roku videos is on full screen for youtube and Raterix videos.

The SDK has a custom video player app example. You could probably code up a short 'preview stream' to play in a mini window as you suggest - and I suppose a few people would use it. I usually know what I want to watch already by name so I don't need previews myself.

Thanks. So, the Roku is perfectly capable of playing video in a mini window, with the listings to the side. So you could scroll down the listings and highlight another listing while the current one is playing in the mini window.
Is there any reason why no channels use this format. Some of the youtube videos would look a lot better with the mini screen, others would look better with the full screen. At least the option would be nice. The free Hulu uses the same format, with the option for a full screen. I suppose I will continue to use my Panasonic blu ray player for some youtube videos.

It's a lot tougher to set up than the built in options. There is also increased lag and you need to handle scrolling/selection yourself. Those would be the main reasons that come to mind.