I finally jumped to HD when Dish picked up VOOM. I have been anxiously awaiting the expanded VOOM. I recently picked up a 942 on lease primarily to watch and record VOOM content.
But if VOOM goes to 1280x720p, I will seriously consider dropping VOOM. The only way I might consider staying, is if VOOM themselves is converting their HD content into 1280x720p, that if their movies, etc., are natively 1280x720 and thus preserve all of the original resolution. A la ESPN being in 1280x720.
But if this is a downconversion from VOOM 1920x1080i content to 1280x720, then that is not acceptable. This will be worse than 1280x1080i. In fact, it is almost a worst case scenario. With only going to sub-HD resolutions, like 960x540, being worse.