Hi just found your forum today - great resource!
Had my Desire Z for a week now and was using a screen protector supplied with a cheap ebay case I bought. That screen protector was easy to fit mainly because it is was obviously smaller than the screen itself. The downside was it was very rigid and thick. I had to lift up the edge to remove a dust spec and it became permanently bent up at the corner a bit with a small air gap. If I had more than one of them I'm sure the second would go down ok. In use it seemed the biggest grease magnet out.
Just now fitted the HTC SP P400 and in comparison - very tight fit. No tolerance at all so the first protector was scrapped discovering this. (i'm a bit ham fisted anyway). The second one went down with almost no problem and now looks great. Good transparency and it seems less of a grease magnet than the cheapie.