The things burst into flames for no apparent reason, and in the end you are left with a piece of useless crap. Most of the time.
As you can tell from the previous sentences, my experiences with these types of computers have been quite ugly. Most of the time, I tend to miss keys whilst typing on them left and right, especially with these MacBook keyboards; those are absolutely awful. There's also the inconsistencies in touchpads: MacBooks still have that separate button, MacBook Pros have the type where you must push down to click, and then there's those lovely Synaptic models. I'd prefer mice to any of those touchpads any day.
What I'm really concerned about is the hardware inside the case. Because notebooks these days are rather cheap, meaning a hell lot cheaper than a 1990s era Toshiba Satellite back then, when a hardware component becomes faulty and/or simply becomes unusable, the consumer may simply buy a new computer and leave the old one in the dust. There's one major source of e-waste right there. Hello environmentalists?
But if you are those who are keen on getting the most out of your hardware, like me, and would prefer repairs over clean-sheet replacements, expect to grumble a bit. Compared to people certified to mess with desktop computer hardware, those in the notebook business number a bit less. A major reason for that is simply how notebook hardware works: parts are small and even the slightest error can basically render the whole computer useless. For example, the pins of notebook hard drives are especially prone to shorting, so repair procedures may involve more equipment than a comparable desktop repair.
Apart from repair, there's not a whole lot of ability to customise notebooks either. The fact that a lot of parts necessary to run a notebook must fit in a confined space precludes many customisations that can be done on a desktop. Forget about overclocking the notebook CPU when you know that all you'll do is burn the computer down. Those Western Digital 1 TB hard drives may not fit in your hard drive bay because they're slightly thicker than lower capacity drives. And there's plenty more you can't do on a notebook that can be done on a desktop…
You get the idea for the "unless absolutely necessary" part.