Operating System & Software
Windows XP or Linux? If the latter, what kind? There are a few potential solutions:
1. Windows XP - Unlike its much maligned successor, Windows XP is a mature, fast and familiar operating system that already works very well. People like it, there are thousands of freely available applications for it and it has vast hardware compatibility. This makes it a safe choice.
2. Linux - Since the beginning netbooks and Linux have been together, yet of late Windows XP seems to have garnered a foothold in the market as people demand more flexibility. What is needed, then, is a Linux OS that has the ease of use of current distros (ala Eee PC/Acer Aspire One) but with a little more freedom. A potential answer is the extremely promising Ubuntu Netbook Remix, but until it's more widely used it's hard to come to a conclusion. Most vitally, however, what is needed is an iPhone Application Store type platform so that users can add new programs quickly and easily, without recourse to the often tortuous installation processes used in Linux.
3. Both - Then there's the compromise solution of Windows XP with a small instant boot Linux element available as well. This may well tick many people's boxes in terms of flexibility and knowing Asus' use of this technique in the past, one can reasonably expect it to do something similar in future netbooks and for others to follow.
So, what about my Ultimate Netbook? Well, logical though the final solution is my heart says Linux only is the way to go. It is, after all, the original netbook OS. What we need, however, is as suggested before, a development community and platform into which many weird and wonderful applications can proliferate. Applications designed specifically with netbooks in mind and with easy one-click installations. And if not Ubuntu Netbook Remix, is there a place for a Google Android for netbooks? I'll leave that one up to you...
This is a no brainer. One of the abiding advantages Eee PCs have had of late is the use of six-cell batteries, when all others have relied on just three-cells and four-cells. Having a six-cell battery more or less guarantees, at the very least, four hours of battery life and with prudent use this can go as high as six, seven and allegedly eight hours, too. This is the kind of battery life an ultimate netbook needs, so six-cells is the way to go.
Size & Weight
A nine inch screen settles the size aspect fairly simply, so then there's weight. Having a six-cell battery probably rules out a sub-1kg figure, but as close to this figure as possible should always be the aim and less than 1.3kg the minimum requirement.
This, of course, will always vary depending on region, but for the UK £350 or less is the benchmark. In an ideal world I'd say less than £300, but if you want the best netbook possible, you're probably going to have to pay a little more.