The notebook was the solution to bringing work home. However, with a computer at home and access to your files at work, the need for notebooks has evolved. They are now required to stay connected when you are traveling outside the home or away from your desk.
However, notebooks are not designed for maximum portability — they were designed for maximum functionality, then made portable. Portability and instant access belonged to the PDA, but many people didn't want to carry another yet another device around and the applications were simplistic.
Instead, the replacement is coming from a surprising source: your cell phone. The first generation of smartphones were more like PDAs that also had speakers so you could use them as phones. The second generation includes some units, such as PalmOne's Treo 600, that are more like phones with PDA functionality. Combined with Sprint's cheap unlimited data plan, it is always carried and always connected to the Internet. This means it is slowly taking over functions from the notebook.
I just realized I have never told you all something. You probably won't believe this, but I don't have a cell phone. I think I am the only person in the world who doesn't. People ask for my cell number and look at me like I am an alien when I tell them I don't have one. I have a PDA, a flat panel monitor, two digital cameras, a digital voice recorder, multiple robotics kits, and multiple computers which I hope to hook up to a home network if Santa brings me everything on my list (Mrs. Businesspundit take note). But I rarely talk on the phone, and since everyone around me has one, I usually borrow one to call if I am out somewhere. As my business gets started in the next few months, I'll have to get one, but for now, there is a kind of warped pride in being without. It's compounded by the fact that I am above average in the tech savvy category, having an undergrad degree in Electrical Engineering and a background in programming and chip design. And I'm only in my late 20s, so I'm not some old fogey who is afraid of tech. I guess it is the introvert in me who doesn't want to be constantly bothered by other people. Anyway, if I do get around to buying one soon, maybe I'll get a good plan and forget about that new laptop.