This trackball actually has 2 laser sensors in it. Yes it uses lasers, not LED's. Nowhere is that part mentioned on any of the Kensington provided information. This is quite easily the best built trackball I've ever seen.

Since I use Linux I don't use the crappy Windows software, but I can still map any of the buttons however I please. The top 2 buttons work perfect in Linux after support was added to the kernel for them. ( =2.6.30)

I had the previous model of the Kensington trackball (the one with the coffee grinder scroll wheel) and I can say that this new Slimblade model is a remarkable replacement over the old one.

The scroll wheel has a small audible 'click' to it provided by an internal speaker (since the wheel itself is fully electronic by spinning the ball laterally) which is a nice touch.

"Unlike most mice these days, trackballs don't have scroll wheels."

Um... where did you ever get that impression? Logitech currently has three trackballs with scroll wheels (out of four). Now you are correct when you limit trackballs to Kensington models though. This is because as far as I can tell (from their current trackball lineup) they don't have any with traditional scroll wheels.

The limited customization options on the slimblade buttons is EXACTLY why I took mine back to the store for a refund.
There is no excuse why the button functions shouldn't have been adjustable from the start. I really wanted to like this product but I ended up going back to their older model the Kensington Expert Mouse trackball.
Why the "advanced" slimblade doesn't have customization options I'll never understand.

Unlike most mice these days, trackballs don't have scroll wheels

It is obvious you haven't looked at many trackballs.

My A4tech has two scroll wheels and three buttons - only drawback, it's not left handed.