The notebooks that I have experience with are the ones that we use at the company I work at. Its all HP business models. With the exception of one perticular model, they have all proven to be fairly stable. At the moment I have an 8510p model, which is really nice. Only problem I have had with it, was that the graphics card sometimes shut off, but it has been fixed with an update from HP, so now its running really well. All in all we have somewhere between 8500 and 9000 laptops, I can't remember the exact figure. And we do have units that breaks down ofcause, but mostly due to people installing crap onto them or throwing them around while they are running. People just don't really care about the hardware when they haven't paid for it themselves, and when they know that it will be replaced without questions. HP has two lines of laptops, those you buy in supermarkets (pavilion,presario) and those you buy from real computer stores (business notebooks like the ncxxxx,nwxxxx series). The business models are more money, but you get more stable units, although not always the latest most fancy features.
