Asus could have done better
First off - it has to be light enough to be carried about in a bag without caring - I think 1KG max should be the aim.
Second - Ubuntu (Remix) should be used. A full-fledged OS miles better than any version of Windows - and it runs beautifully on these machines. Mass of applications and a huge community of users to work with to enhance/extend things.
Third - No HDD - this cuts down noise and power usage.
@Michael
Try the Dell Mini 9 which sounds like it fulfils your specs - I picked mine up for £220.00+VAT.
All I need is a client machine because I mostly work on LAMP servers. I was able to use the Mini 9 as my main machine for several weeks - I plugged it into an external monitor, keyboard and mouse at work. All I need is standard Ubuntu, Foxmarks, import keys, connect to mail server and I'm sorted.
As a brucie bonus - it's dead easy to take away with you - and will even fit inside the normal safes used in most hotels.
Mind you - it might be worth checking the Mini 10 - currently £199 - or the Mini 12 which unfortunately seems to come with a HDD only.