First a comment about the Bell Express Vue HD receiver. Is that like a satellite or cable box? If so, don't be upset that it can't do 1080p because there's no such thing as 1080p via broadcast. Neither from satellite nor cable, nor OTA TV. Not for a few years anyway and maybe never, so I've read. The only source for true 1080p material is from a Blu Ray DVD or from a gaming console.
I am really new to the HD world, only having had my HDTV (Samsung LED DLP 1080p) set for a couple of months. So my comments are from a newbie. But I've done *tons* of research and have spent *hours* watching HD programming both in the store and at friend's homes.
My conclusion? Well, my TV is a true 1080p set, so I have all of the options on the table. My Dish Network HD receiver can be set to send out a 480i, 480p, 720p, or 1080i signal. It does the up/down conversion automatically. I've tested them all with various content. For most content, I couldn't tell a difference between 1080i and 720p, other than the TV noting that the resolution had changed. However, I found a few programs where the 1080i did look a bit clearer or sharper. Specifically, some of the 'show-off-your-HD-eye-candy' nature type shows. Could it having nothing to do with 720p vs 1080i and just be how my TV and DishHD up/down/side conversions are working? Certainly. But since there was a difference, and the 1080i looked better in a few cases, I stick with that on the Dish receiver.
The real differences with HD content comes from the filming & broadcasting, not just the fact that it's an HD channel. Sources vary a lot. Sometimes an HD channel might broadcast 'SD' content, even though it's being piped in via HD bandwidth and recognized by your equipment as an HD show. The BravoHD channel is an example of this. While you're laughing, let me say that I don't watch it buy my wife does, and I'm usually in the same room. So occasionally I glance over the laptop screen at what's going on. Several of the shows on there, even new ones (Project Runway), are NOT really done in HD. Still 4:3 and only marginally better than normal SD quality. A show like that is a horrible demo of what HD is capable of. That signal may be broadcast in 1080i, but the picture quality is somewhere between regular TV and 480p DVD.
Then compare that to some of the jaw-dropping content on the National Geographic or DiscoveryHD Channel, and the differences become quite clear.
Another thing to keep in mind is that FOX and ABC broadcast in 720p. NBC and CBS broadcast in 1080i. So if you're watching one of those networks, that's all you're going to get.
