I dont believe Netbooks are a fad but rather, they have yet to evolve to their intended potential. If you look at the user demographics for these devices, they are greatly driven by younger, smarter, web 2.0 and social networking junkies. These kids will grow up in the cloud and I think that is the most important issue that isnt being properly assessed by the critics.

In the case of the iPod or iPhone, Apple did not invent MP3 players, nor did they invent the smart phone but they made them both A LOT better. If Apple can form-function a netbook with a competitive price tag vs. PC/Linux devices, they could have a real slice of the personal computer market share that has always hovered in the sub-5% space. By using the iPhone Operating System on a netbook, Apple could conveniently plug-n-play with existing iPhone apps offered in the iTunes Universe, giving them a jump-start that is light years beyond the evolution of competing vendors. This trend could become immediately viral, as Googles Android becomes an established OS, and the number of netbook/smart phone applications multiplies exponentially.

With their limited hardrives and nominal processor speeds, netbooks will only really come into their own once the foundation of smaller, lightweight, apps and hosted computing are laid. To their [netbooks] credit, its not so much that they are at fault for being considered a Fad at the moment. Its simply that the infrastructure they were meant to thrive on: WiMax/4G, Cloud Computing, Hosted/Subscription Everything - has yet to have been fully realized.

Additional Reading: 35 million Netbooks in 2009 ; Intel Netbook Blog ; Apple Netbook

Follow-up Comments:

In 2008, netbook sales accounted for nearly 15% of Laptop sales, over 15 million units sold. Considering that the netbook category didnt even really exist prior to 2007, its safe to say that skeptics should certainly be taking notes.

With the slight margins on these $200 - $400 machines, hardware manufacturers arent actually profiting from sales. Likewise, the software vendors still havent tailored their user experience to this trend and consequently, have not figured out a way to make money on it.