Well, RobertB, you caused an explosion of experienced users' comments with your last comment, great work. I don't have any eReader, so I can't very well comment on that, but I *am* admin in software company so I will try to go this way.
1) Betatesting is the key. Look around in computer industry and you will see great examples of *failed* testing, on software and hardware level. Good example is SATA1 versus SATA2 cables for PC's. The only difference is SATA2 learned from the errors of it's precedesor and added "safety pin" so the cable can't unplug by accident or simply by moving such PC. I had seen the problem the second I plugged first SATA1 cable in, so why noone told the engineers and developers? Few betatesters who really do their work and have a brain to use can save you lots of harsh comments and give you a headstart. It could be anything from wrong positioned button that accidently gets pressed to confusing menu design, the only way to find and eliminate these bugs is good planing and good testing. Also, people on this board are experienced and it seems to me most of the latest articles are really good and practical, from users who have experience in this field.
2) Software support - I am not sure you *can* allow custom software in your new eReader, but what about the computer side of this? For example, my Firefox is customized with several plugins which adds lots of great functionability and it's the main reason I use it.
3) I presume you will add computer-sided software, and I would love to use it for managing eReader through it. For example, complete backup of my settings, synchronization with a list or directory on the computer, library management and all those things that would be hard or time consuming to do directly in eReader. I can do it in eReader if needed, but for mass changes, full computers are simply better equiped if there is a software that allows it.
4) File convertions. If the pdf file is hard to display properly, no matter the reason, I want to convert it to another format, for example rtf, doc. To have these functions integrated in software would help a lot.
5) Durability. Truth to say, one of the biggest disadvantage I see in eReaders is that they are simply less durable then normal books. If I buy a device for 300$ or more, and then I loose it half year later because it dropped on the ground, I would think really hard about buying new one. It's just too expensive if it can't survive in good health for several years. Same goes for life expectancy. If the device is guarantied to work for 5 years and another one for only 2 years, which would you choose?
6) I want to be able to customize the accesories for the device. Simply add a list with allowed accesories and price for each one. For example, basic card has 256 MB storage space and cost 5$. I don't want it, so I switch it for 2 GB which cost 45$, but the result is only 40$ more expensive because that 256 MB card is not there anymore. Do I want a cover? Yes, this one is made of nice quality leather and cost 50$, this one is from stainless steel
and cost 5$. I can choose none, or both of them. Do I want more batteries (ability to insert more then one battery as Moz suggested to increase battery life is excelent in my oppinion)? Sumarized, I would like to have complete control on what I am ordering. For me, it's good thing because I get exactly what I want, and I can be sure that it will work together. For you - well, you are the one selling it so more profit. After I complete my order, I get one package with everything I ordered, and I am happy that I have all I need. Of course, it requires reasonable prices, if I can choose to buy an 4 GB card from you for 100$ and same card from local shop for 50$, it's easy to decide. Such buying model have more advantages for you: it attracts people, makes you more popular because of the free choice you give them, and again, improve your chances on the market. There may be even two buying models: buy our "standard package" or for advanced users, select exactly what you want.
7) If your eReader have wifi and can be connected to computers, does it mean you can browse the internet? Integrated browser, mail browser, etc. can go long way in user comfort and increased sales. Map software? If I can't find something while I am in a city, I could have map installed (eighter as simple scanned map or more complicated software found in navigation devices).
8) Software keyboard. I mentioned it before, it greatly increases the flexibility.
9) Third party aplications, if possible. If you can't allow free software modifying, maybe you can allow people to send you such software. There may be a 3rd party software option on your web, with warning that it's not supported by company, allow everyone to download it and install in the device. Let others do the hard programing work and still be praised for allowing it.
10) I am not a friend of solar panels. Maybe because I don't know good ones, I worked with some and they are (or, better, they were) very, very fragile. Maybe now you have good and sturdy panels with good effeciency that would allow the device to be near 100% solar powered, I really don't know. I would have to know more about them and how are they protected. If it worked, though, it would be another great improvement.
11) Good support for newspapers - I don't know if there is some standard they use for electronicly publicated newspapers, but one of the thing I do daily even before I go to work is reading news on the internet from several sources. I wish eReaders could make a difference, why should I power up PC or buying "paper newspapers" when I can read it like any other text on device developed for reading texts?