Last week, I went into Best Buy with an Invisible Shield I had purchased online and paid a guy $8 to install it. I waited till now to post because I wanted to see how it cured. Bottom line? I am very happy with it. It looks almost perfect.
The process took about 15 minutes in the store. One thing I didn't expect was that you are supposed to leave your Pre untouched for a while (ideally 12 hours) after installation. I had planned to run errands after and it was hot, so I carefully slid mine back in my leather side case (the official Palm one without the clip--love it) and left it in there for as long as possible (so that I could take it with me into the airco-ed stores without fear of dropping it or messing it up).
When I left the store, there were a number of small bubbles and what looked to be smears around the front of the screen. The guy told me to give it a few days--time to cure--before I passed final judgment. He also said if I was unhappy with the final outcome, I could bring it back in and they would redo and replace it for free. That's a pretty sweet deal (though maybe he assumed I had purchased it there).
Anyway, a few days later, the streaks were gone and I had two very small and one pretty large bubble left. A few days more, and the two small bubbles were gone. The one that was slightly larger appears to be getting smaller now, so I may end up with zero bubbles. In any case, the screen is clear of bubbles, and the one that is getting smaller does not get in the way of anything or bother me at all.
The only thing that does bother me a bit is the way the IS fits corners. I suppose there is no way around it, but the fact that there are seams that allow the screen to grip around the curve of the corner means that you lose the perfectly smooth, stone-like curves there. That's a bummer, but it's not too, too bad. They are very small seams at the corner, and I'm getting used to it.
If you want to read about all of the screen protecting options, check out this thread at PreCentral.net.