I wouldn't use the squeegee at all. I've installed it twice on a 3GS and I'm convinced using it would create additional problems by stretching (even so slightly) the material to the sides. That promotes it to eventually want to pull back to the center and pull up off the corners. I think this will happen a lot less with i4 because the back is flat, but there's really no reason to use it.
You just need a tiny bit of spray (1-2 pumps) from 12-14 inches away just barely misting the surface. Lay it down, position it and very very slightly use your finger to move out any big bubbles. The tiny ones will evaporate out after 48 hours or so.
My prior installs lasted lasted 8-10 months on mine and my wifes phone, but eventually started peeling up on a corner. That drove me crazy, so I'd wind up peeling it all off. I don't see that being a problem on the new phone unless you stretch it out and I think using the rubber tool will do that and possibly mark it up in the process.
I plan to use the Wrapsol with an Incipio feather case. Primarily use using the Wrapsol to protect the glass from scratches when dust gets under the case and when I have to remove it to put the phone in a windshield mount.
