I agree that ultraportables, like the Q40 Ramazan mentions, have a completely different niche as compared to netbooks, but as you say, a £300+ machine is not that chuck-about-able at all, and in all fairness, you can find older £1000+ machines for £150 on eBay as well. I use my old Vaio TR5 that is 5 years old for netbook tasks, but I just love that it is the same weight range (1.4 Kg) and same dimensions (10.6 inch screen), but with a great keyboard, and with 1280x768 resolution, and the screen is of such a high quality that it is entirely usable. It is no longer my main laptop so I don't mind it taking a bit of a battering either, but it really is a great little machine that I will be sorry to see die off.
I would like to see how the Atom handles an Oracle instance which I need for work, as the little Pentium M ULV could work happily away with it, and the higher rez allows for useful spreadsheet viewing, but then again, those tasks are not what netbooks are designed for! Unfortunately, with the growth of netbooks into the larger, pricier form, such as the Acer Aspire 751, people will be thinking of them as small notebooks and that may well turn people off them.
As per other posters, it will be interesting to see what the new, small, ARM based machines will do to the market - I have noticed they are growing as a sector over in the Far East, but that region always produces many items that never make it over to the West...