I like the hill programs best, where you start off fairly flat and get progressively steeper hills. It's not realistic, because you go up these hills, but on a treadmill you never get a downhill. It's a bit misleading, because downhill running poses its own set of challenges, and a treadmill just never gives that to you.
Perhaps I like the hill programs partly because I live in Chicago where hills are in short supply. Most of my distance work is on fairly flat terrain. When I look at doing triathlons or marathons in other locations, I always look to see what kind of changes in elevation occur on the route. I know I just don't have the real hill training under my belt.
Rhyme of the day:
I will, I will, I will
Get over the next computerized hill!