I've had my Illiad V2 for nearly a month now. And basically I find the pen a really useful feature. I have used it to take some short notes but it really excels at allowing you to sketch something. In terms of fineness it can write a 1 pixel wide line which equivalent to a pen with a .16 mm end point. When I write normally is use either a .5mm (fine) or 1.0mm (medium) point pen so I'm never really using it at its finest resolution. For me at least I find I can draw a sketch on the screen using the 'notes' function and have it print on an 8.5 x 11" sheet of paper and still look like a sketch and not a pixellated mess (like it did with my Palm V, and my Newton MessagePad 120 before that). Since you can use any PNG image as the 'paper' for sketches I made a couple of images with pre-built identifying boxes (like in the lower right corner of an engineering drawing) and I can label the sketch there and when it prints it looks, well it looks like I took a piece of vellum and sketched on it. The other thing is that I have a 6" metal ruler with a cork back that I can lay right on the screen to draw nice straight lines.
So that being said, there is noticable lag between starting a line and having it appear on the screen. Probably about .25 - .5 second (I've not measured it) which takes getting used to. That is what makes it hard to take notes on. You are used to seeing your words flow out of the end or your pen, but on the Illiad they seem to be chasing the pen. I also find that when writing I don't always lift the pen enough for the Illiad to realize it isn't on the glass and so I get a line from the bottom of my 'i' to the point where I was going to put the dot. Writing in cursive works better than printing, readability when printed is quite high and so far it doesn't leave any gaps when I'm writing (so no messed up characters). Its better than the best 'electronic signature pads' but still not as good as writing on paper. I've heard that the CPU is not running at full speed however when scribbling so there may be some easy improvement to be gained here. Tapping a message out on the keyboard is pretty quick.If I can ever get someone to tell me how to compile a GTK application on a non-Linux system I may be able to improve the drawing capabilites with text callouts.
I suspect its a bit pricey for the secondary school set however.