Personally I think it's a complimentary device. Some apps are just going to work better with a multi-touch interface than a traditional keyboard/mouse setup. Judging by the amount of new UI elements it appears you can write some serious, near desktop quality, applications for the iPad. I think a very common usage scenario is going to be using the iPad in conjunction with your laptop or desktop. For example, I think multi-touch web browsing is a much better experience than a keyboard/mouse browser experience. It's just easier to move around pages and zoom in. If I had an iPad sitting on my desk next to my keyboard and mouse I suspect a good chunk of my browsing would be done on the iPad.