The first experimenters who tried to measure the speed of light concluded that light speed was infinite. Their equipment was unequal to the task of measuring something so very fast. In v = d/t, the t was too small no matter how big they made the d.
Similarly if you were to take the ratio of effective presentations (PowerPoints) you've seen to the total number of presentations you've sen, you would be forgiven if you concluded that "effective PowerPoint" was an oxymoron. (The "effective" number too small and the "total" number total too large.)
Effective presentations do exist. Garr Reynolds hosts a weblog devoted to Presentation Zen. He offers fundamental principles for success that can be found here.