Well I thought I'd post my thoughts on this...
I bought an Invisible Shield one from Zagg, went for the full back and sides protection too.
Awkward to fit, but got there in the end, took some time to get the back and sides to fit correctly. A couple of tiny bubbles on the front screen disappeared fairly quickly, but was still left with some on the rear of the case.
So with everything fitted what was it like? Horrible IMO. I didn't like the feel of the phone with the back and sides on, you felt all the edges and the surface of the protector material has a slightly tacky feel to it that just attracted bits of fluff when you put it in your pocket, but I stuck with it for a couple of days.
After two days the rear sticker still had bubbles in it and looked naff and I decided to bin the rear and side stickers and just leave the front one on...
Which brings me to the front protector, it's quite a thick sheet (I'm sure it would protect the screen if I set about it with a knife, but I'm not likely to do that), has a slightly orange peel effect to it, doesn't let your finger run over it as well, and definitely cuts down on the screen sensitivity.
So in the bin it went, money wasted, and I now have one of these on
MFX Screen Protector - Samsung I7500 Galaxy
Very smooth, clear screen, and much easier to apply.