I see that when exporting video, Lightroom versions up to 4.3RC support MPEG levels up to 5.1 but not the highest quality MPEG level 5.2. I like to request that MPEG level 5.2 be supported for maximum quality - thanks!
And just to explain a little further, the supplied video presets are somewhat restrictive so there are a lot of us who are making our own video presets and making them available for others to download. Within these presets one can specify the max bit rates, frame rate, MPEG level, etc. When one tries to use the latest greatest MPEG level 5.2 lightroom won't use it. Lightroom appears to only support MPEG levels up to 5.1.
It would also be great if Adobe offered more video presets to begin with. A larger variety of frame rates (including slow ones (1fps, 2fps) and resolutions (up to 4K).