Update:
I've played with the new formats a bit and it seems format 5 (240P, flv) is not supported by the wdtv, so I reverted it to 18 (360P, mp4).
With regard to navigation - it seems it doesn't make any difference if I try to navigate inside a flv or a mp4 inside the youtube interface - it can FF/REV only inside the buffered area, so my comments are irrelevant.



