Next, the "PerfectStroke key system" and "Incurve Keys" really are comfortable and make typing easier. I particularly like the way the key feels when you press down. You get a very small amount of feedback almost resembling the old IBM keyboards, but without the loud clicking. I agree that it is a bit like tapping on a laptop. The big difference, however, is that the keys on the k750 are much sturdier than those on your usual notebook PC.
As for the connection, I was a bit worried that the new super-small "unifying receiver" would not provide adequate signal. This is incorrect. In fact, this small transponder works much better than Logitech's older stick version. It is on the back of my pc and so has to see through an aluminum computer chassis as well as a wooden desk, about 4 feet total distance. I've never had a problem with the signal on either my mouse or this keyboard.
Finally, the software for the keyboard is pretty much what you'd expect. You press the sunlight button and a dialog pops up on your computer telling you the "LUX" (amount of light) your keyboard is getting and how much battery power is remaining. There is also a function key which you use in combination with the top row of keys to do things like open your internet browser, pause a song, mute/increase/decrease the volume, etc.
One downside, according to my wife, is that it looks like I'm using a giant old-school calculator. I think this is not true at all: the solar panels are a dark red while the keyboard is black. This causes the solar panels to not really be noticeable unless you are looking for them.
