Lack of progress and innovation: Before Apple shipped the Retina iMac, the best laptops had the same resolution displays as the best cell phones. Typical laptops were both slower and lower resolution than phones.
Confusion: Buy a 4k display. Figure out what graphics card you need. DisplayPort, MiniDP, DVI, VGA, HDMI, versions of all of those, "dual link," maximum graphics card resolution. It's a disaster. Things don't just work. I called Dell asking what would be needed for a quad monitor 4k setup with Dell monitors and computers. They didn't know, and they didn't know who might know. Dell has Inspiron, XPS, Alienware, Latitude, and Precision as major product lines, and most of those have 3-4 sublines. What's the difference? Even Dell doesn't know (hey, Dell, did you know your reputation is set as much by your business stuff as consumer stuff? People don't differentiate). Resolution? Always labeled by weird labels like "SXGA" and "SXGA+." If you want the actual resolution, best of luck. And don't get me started on processor speed. What does i7-3500 even mean? If the config options have an 8 core with 4MB cache and 2GHz, and a quad core with 8MB cache and 2.2GHz, and one is of a different generation, I doubt even Intel knows how the speed compares. Going for the cheapest always makes sense, given how long it would take to figure it out.
Lack of choice (or nice products in general): The lines are close enough to each other that the computer you need is almost never there. The old Inspiron 8000/8100/8200, and corresponding Latitudes had interchangeable parts. You could configure to order. Today, want that high res display and a trackpoint? Can't get it. Or want that in matte (not glossy?). Tough. Want to drive multiple high-res monitors from a laptop? Boohoo. Don't like wide screen? Well, we don't like you. None of those options, individually, are big sellers, but the lack of any of them demolished the high-end computer market.
Consumer-unfriendliness: It's 2014. Why do I need to lug my power adapter with me? Couldn't we get a standard that worked with Dell, HP, IBM, and everyone else, and when I go to a conference, hotel, or family, I just plug into their adapter? Of course not. It would hurt power adapter sales. How about standard batteries where it makes sense? Even if I upgrade a Dell to a newer Dell, my batteries all go obsolete.
It's no wonder PC sales are dying. This stuff isn't rocket science, but the organizations making PCs are f-ed up enough internally they can't even get any of the basics right.