Preliminary Hardware Requirements for Digital Sketchbook

I've begun to put together a list of requirements for what I feel would be hardware that would support the vision of the designer's sketchbook. The following is a list of hardware requirements for a computer system that would support this sketchbook:

1. The system must be extremely portable (i.e. under 3 lbs) if you want designers to have this tool around them at all times. In fact, Alan Kay, through careful studying, has noted that 3 lbs is the optimal weight for a portable computing device.
2. The system must have a long battery life (at least 4 hours). Designers may not be able to find a power outlet when they are inspired to sketch out a new idea. In addition, carrying a power adaptor around with you, adds to the weight of the machine.
3. Pen input via tablet is a must have, as designers typically sketch out their ideas free hand with a stylus. Touch input is something that is nice to have, but not absolutely necessary. In any event, this capability must be built into the device, as designers won't carry an external tablet that adds to the weight of the device, and for which they could easily leave behind.
4. Screen size of at least 10.1 inches (if not more), as designers typically need a canvas the size of a regular sheet of paper or larger to sketch out their ideas. While there have been stories of designers sketching out ideas on the back of napkins, this is usually the exception not the rule to sketching out ideas wherever you are.
5. Reasonable hardware performance. Designers don't have to wait for the sketchbook that they carry around with them to boot up, and load the sketching software. Therefore, why should a digital version impose this constraint upon them? The amount of time that a designer should wait to get back to the sketching software should be no more than 15 seconds.
6. The cost of the system should be relatively inexpensive (less than $600), so that it remains in the budget of many designers. In addition, if the system is expensive, designers will feel less inclined to bring the sketchbook with them for fear or damaging or losing the system. To reiterate, this system should encourage designers to have this system around them at all times, as ideas can happen at any time and anywhere. I know that this may be a difficult requirement to achieve, as it is possible to built a system that meet netbooks s the above 5 requirements in the thousands of dollars. However, I believe with the rise of and other inexpensive computing devices, this may become possible in the near future.

To sum up, the system that I am looking for to build this designer's sketchbook would meet the following abbreviated requirements:

• Extremely portable
• Long Battery Life
• Pen input via built-in tablet
• Screen size of at least 10.1 inches
• Reasonable hardware performance
• Priced Under $600

I now ask the community, are there any computers out there that meet these specifications? In addition, are there any other hardware requirements which designers feel are essential and which I have omitted?

Let me know what you think!