I've used earlier Microsoft ergonomic keyboards previously, and liked them very much. I wanted to update to a USB model, and so I bought the 4000 model without hesitation. Unfortunately, as other reviewers discovered, the space bar is difficult to press down.....so much so that it makes typing rather difficult, which is exactly what an ergonomic keyboard is supposed to help alleviate!! As such, this keyboard is all but unusable, unless you type with only your index fingers. If I could give it zero stars, I would.Did MS even *test* this product? It's a disgrace that they would release something that has such a glaring deficiency.....but then, it's Microsoft, so why be surprised. Too bad because the rest of the keyboard is really pretty good.