I think everyone knows already that I'm a big fan of High Def and that for all kinds of reasons I think High Def is one of the most exciting things to happen to indie film making since the first lightweight 16mm cameras were developed in the 1930's.
However, that said, High Def is a creative choice or as is more often the case, a budget choice.
Film isn't dead and it's unlikely too as a medium, because it has unique visual qualities. Given a big enough budget, 35 mm Film is going to out perform High Def; given a tight budget, it often works the other way round.
What makes High Def interesting is that it is the first digital format that can stand up to a full size cinema screening, without the picture falling apart. So, if a cinema distribution is on your wish list, but you have a small budget, High Def is a good choice.
The other factor that makes High Def a good choice is that the High Def TV market is just about to boom and as it current stands, distributors are taking a keen interest in any High Def product. However, that said there is a lot of mis-information out there about High Def and it's worth doing some serious research. For instance, although Final Cut Pro HD, can edit High Def footage, it can't take the image in at full resolution. The only way to do that is to purchase a High Def video capture card, current retail price £15,000.
I think the thing to remember is that although format is important, it's not as important as what you do with it. Script is more important than format, as is performance, as are basic production values and good sound. In fact, more important than all of these, is understanding where your film belongs in the marketplace and the rules that buyers apply.