Thanks guys.
@Jim
That's odd -- the backbuffer isn't getting cleared on your machine... have you got DX10? Please let me know if playing around with the drivers sorts it out. I'll post up another version that clears things manually as an interim solution (hopefully) but it'll be a little while as I'm a bit tied up (not literally, unfortunately

) at the moment. I've also been hideously lax about commenting on the other entries so I'll fix that ASAP too. Not enough minutes in the day currently.