"Star Wars" is such a true classic, it's ranked by the AFI as the 13th best motion picture of all time. Watching the prequels first is like watching Casablanca, but first watching a parody of the movie that gives away everything that is going to happen in the original, sapping a lot of the drama from it. It's the same reason that people who record a football game don't want to know the final score before they go home to watch it.

It's pretty irrelevent when and if you see the prequels - as long as you don't see them before Star Wars and Empire Strikes Back.