Depending on their construction, you may be able to attach them through a solid part of the back of the cabinet (not just a thin dust cover backing) into the wall studs.

When I installed my base cabinets I did not have to attach them to the floor, just the wall. I choose to put down plywood under the cabinets and appliances instead of placing them on the flooring. I would think that this is what you will have to do if you are installing an island and the cabinets must be anchored to the floor. Trim will cover the expansion gaps.

Makes sense to me to end the flooring at the cabinets and use plywood under them---saves money, allows fastening any way you wish, and that allows the appliance spaces to have the same level as the flooring---very important.

Thanks everyone! I agree putting everything on plywood is going to be cheaper and allows for more flexibility with securing the cabinets. Also, we will have an island, so we'll have to use plywood there.
The only advantage for us for using wood flooring under the cabs is that we can be installing the flooring right now, while the cabinets are being manufactured. Using the plywood, we'll have to wait for the cabinets to be made and installed, before we can start the flooring.
Re the appliances, sometimes I see the flooring material underneath them. Usually the frig, sometimes the range and DW as well. What do you think of that set up?

Under the appliances I ran the plywood only to where the legs of the appliance are and put flooring up to there so that the legs rest on the plywood and the edge of the appliances overhung the flooring.
You really do not want to put the flooring down now as it will take a beating when you install the cabinets and appliances. Putting the plywood also gives you the opportunity to level the floor which makes installing the cabinets so much easier. Instead of leveling each cabinet you can shim the plywood to level in 8 foot sections, much easier than doing the cabinets in 24"-36" sections. You can chalk your lines on the wall off from your level floor and install the wall cabinets first so that the base cabinets are not in your way.

When I install floating floors, I use the flooring in fridge and stove spots---just to make the job faster. The DW space depends on flooring height and countertop height. If the flooring is too high, the DW may be quite difficult to remove/replace. On a new construction job like yours, that problem is nonexistant.

Hi, it's me again, the OP. I just thought of another issue. We have a concrete slab subfloor. Is it ok to lay plywood directly on top of that? Would I need a moisture barrier first??
I know for our floating wood floors we're using a combo pad/moisture barrier underlayment.
If I need a moisture barrier under the plywood, gads, that seems to complicate things! Run the same flooring underlayment under the cabs? In one contiinuous sheet? I can just see the flooring underlayment getting shredded by all the traffic from installing the cabs.

pchow,a similar question came up in the flooring forum recently and one of the flooring pro's said that plywood directly on concrete is not a good idea, he recommended a vapor barrier. I would use the same underlayment as you are using on the flooring, this would keep both the floor and the plywood at the same height.

Floating floor are helpful in remodeling and providing new look to the house. May be it is costly but seem to be quite helpful for those who want to have a perfect house along with saving rest space of house from unwanted coverage from things.