why do my new hardwood floors squeak

A product called offers a simple solution to eliminate squeaks from the top side. The $20 kit includes a tripod tool, bit, stud finder, and screws. The screws are coated with wax to drive through carpet without catching strands and causing a run. You use the tripod and bit to drive the screw through the floor covering and subfloor into a joist. The screws are prescored 1 inch from the top. So when the screw is in place, the tripod snaps off the screw head so it won't stick up, but the threaded part holds the floor to the joist.

This works for carpet, wood, vinyl, and linoleum floors. You'll have to fill the hole left in wood floors with wood filler. Linoleum and vinyl will expand slightly to partially cover the hole, but they won't hide it completely. In the end, you'll have to decide if you want a tiny hole (which you can strategically cover with a rug or carpet) or prefer to live with squeaks.
My freshly installed (still unfinished) harwood floor is squeaking moderately, and I am wondering how much is too much, or if there should be no squeaks at all.

A carpenter friend and I just installed the floor, 500 s. f. of 3/4 American Cherry hardwood, 3. 25 wide, in my new addition. We followed all the advice we could find - prepped the subfloor well (3/4 T G), covered it with 15lb tar paper, face nailed the first row about 1/2 from the wall edge, blind-nailed the rest with a manual 45-degree floor nailer from a local flooring store, using the specified nails. the boards appear to fit together snugly though there are perhaps 2 spots on the whole floor where we have very slender gaps between a couple boards (playing card width) -- these run for about 18 each.

The squeaks don't seem related to those gaps or anything in particular.

They aren't horrible - no big pops. But I'm kinda surprised it squeaks at all. It felt solid as we went along, and I thought squeaking wouldn't set in for a few years. Are my expectations unrealistic here? If I want to minimize the squeaks, can I do it by strategically face nailing (or screwing and plugging) a few boards, or will I have to go after all of them? All is not an option for me -- I'd take the squeaks over placing that many visible fasteners in the new floor.

But if I can help the problem by securing a few key boards, I'd like to try that before I sand and finish the floor. (Unfortunately b/c the foundation crawlspace is tight and hard to reach, securing from underneath with screws is only an option for about 1/2 the floor, and it's a very unpleasant task. ) I'm sure it's obvious but this is the first hardwood floor I've installed.