I frequently get this.
I can be in a list and have to select one (like in Market and I want to D/L an app, I tap it and the screen scrolls up by 1-1/2 pages. I go back manually, tap it a bit harder, same thing. Repeat several times. Then bam it works. Or I can be on the home page and tap an app -- nothing happens. Over and over. Finally it loads. Or I press hard enough that the item highlights itself, let go and nothing happens.
I've tried to demo this problem to Verizon personnel...but, of course, it doesn't happen then.