Hey Jay, I havent noticed any whine while slowing down, but I've only had my Maxima for about a month now and I really havent driven it with the windows down. I am going to do so later on to see if I have the whine.
As far as the CVT goes, I have noticed the same thing as you. If you are fairly light on the pedal the car upshifts pretty quickly and keeps the rpm's down. This tranny is a very different animal than the normal 5 or 6 speed tranny, so my theory is that this is normal. Even in a regular 5 or 6 speed auto, if you are light on the throttle, the shifts come much quicker and keep the rpm's lower than if you stomp on it for heavy acceleration. With the CVT the gear ratios are continuously varying, hence the name CVT, which I believe further enhances the feeling you are getting. In other words, the modern tranny both CVT and conventional are very smart and they know by your throttle input what you are trying to do. Having them work this way helps with fuel efficiency. You dont want the car to be screaming up to 4 grand for every shift if it is not necessary as this would use more fuel. If you dont want to feel lame off the line, you just need to use more throttle input, this will hold the shiftpoints higher. One thing I have noticed about the car is that it doesnt like to be floored and it seems that if you put the engine much above 4500 to 5000 rpm's you are far enough out of the power band that it doesnt seem to accelerate as quickly. It seems to perform better with a steady rolled on throttle.
As far as your MPG's go, mine are right on par with yours. I will admit that it is a little dissapointing, but most people dont realize that the EPA testing in no way duplicates real world driving so the figures are kind of inflated a little. This is supposed to be corrected for the '08 model year, when they change the testing standards. Basically you are going to see a decrease in vehicle mpg ratings across the board, which will probably make the numbers a little more realistic. I would say the only way you are going to see 28 mpg in your Max is by driving the whole tank of fuel strictly on the highway and by keeping your speed at no more than 60 to 65 mph.
I will post back on the whine after I get a chance to check for it.