Wait, you have a bug tracker?I don't remember seeing these issues reported before; tearing in Xv is a known issue (for most vendors, not just us) but you should be able to get good tear-free playback through OpenGL. If you haven't already posted details about the black lines on your windows can you start a thread or point to a bug ticket somewhere ?
In any case, the Xv tearing is an fglrx-specific issue unlike what you think. It doesn't happen with radeonhd, it doesn't happen on Intel GMA with the DRI drivers, and it doesn't happen on nV cards with either their binary blobs or the nv driver. Yes, OpenGL is what I'm using now, but it requires that the player have a properly optimized OGL backend -- you can forget about MythTV.
Oh, and I forgot to mention that fullscreen FLV playback via Adobe's Flash plugin for Firefox is unusably slow. The video is a slideshow and the controls are so unresponsive that every time I try it I have to resist the urge to tab out to a tty and kill X outright. This doesn't happen on nV cards with their binary blobs.
-E- Another (minor) issue I just remembered: If I tab out to a tty and kill an OGL app, the screen is corrupted. It does correct itself when tabbing back to X, at least.