In order to round out this thread for the archives...
I picked up my roll of Delta-Fl and sealing tape from Lowes on Friday night, and spent Saturday installing it. As I referred to in the instruction link above, laminate flooring (with it's underlayment) can be installed directly over the top of Delta-FL. Costco had a sale on laminate flooring, so I bought ~340 sq. ft. of that, and 2 of the associated installation kits, which comes with the spacers and tap-blocks, along with 150 sq. ft. of 1/8' foam underlaymnt/vapor barrier.
As it turns out, Delta-FL is not what I expeted... I thought it would be more of a stiff foam, but in reality it's a thin-wall plastic (actually HDPE). It comes in a 5' wide roll, and has ~5/16" tall 'dimples' in it that provide the actual shock absorption.
Laying it is relatively straight-forward, I'll let the previous instructions link provide the detail there. It did tend to want to buckle and ripple a bit on the floor, but I could "walk" the ripples out away from the laminate as the rows were progressing.
With the 1/8' foam on top of the Delta-FL, there's a total ~7/16" of underlayment, with the laminate flooring applied directly on top of it, floating. No plywood/OSB, screws, etc.... just snap the flooring together on top of it (altho getting the floring together was a 12-hour chore in itself).
The end result is fantastic. Just what I had hoped for - a nice surface over concrete that has the feel of a framed floor. After some extensive scientific validation (we jumped around on it a while), it should really fit the bill as a dance-surface for my wife's studio. the concrete pad was not exactly level, but the underlaymeny helps soak some of that up. No odd sounds or feels to speak of.
I'd highly recommend it for applications directly over concrete floor that don't require you to sacrifice a lot of height.
A few pics of it start on page 7 of my site
PS- teenie, you said
"In my case the plywood is screwed down to the slab and in fact than compresses the delta-fl but not quite flat. "
I imagine if this is true, you've eliminated much of the value that Delta-FL provides.