Laptops really suck at very heavy computational processing. Desktops still hold the top of the hill when it comes to being the device you want for doing extreme computing. Laptops are great for simple development or social updating, maybe some media but past that you really need to move up to a desktop. Tablets have even less power then notebooks so unless your only writing a document and watching a movie, your out of luck. It would be great to blur the lines but were still at least 10 years out from it happening.
Agreed, my tablet has significantly reduced my "casual" computer usage, (when I behave like Joe User, email, web, social, etc.) but it's next to useless for the needs of a code geek. (Though Orion might change that.)
I think that the given a bluetooth keyboard average user can probably use a tablet to accomplish 98% of what they need, but personally I also need a high-end laptop for demos and mobile problem solving as well as a desktop with gobs of RAM and drive space for real work. (Developing, debugging, DB server, etc. etc.)