It's not really a cheat because it was placed into the game by the designers themselves for intentional use. How often you use it, if at all, is entirely dependent upon you.
I think a common complaint about Morrowind was that it often involved endless trekking through wilderness, Although fast transport was available between the major cities, much of the game required travel to non-city locations. And that travel was slow. Perhaps Beth created the more flexible system of fast travel in Oblivion to answer those complaints?
So far I have only used fast travel twice. Once just to see what it was like. And a second time when I had to escort someone who was unusually slow. That second time might have been a cheat.
In general, though, I think good reasons exist for fast travel. I am not using it because gathering ingredients is a major concern of my character. But I think Oblivion allowing us to decide whether to use it or not is a good thing. Flexibility in game play....awesome!