I have a 2nd hand G1 I got from eBay that's solid as a rock. I'm not sure which device people are pointing their fingers at when they level this argument at HTC.
It's a consistency issue. Too much process variance.
I have a nicely built Evo, but I've heard of many others who have screen separation issues at the bottom. Easy to spot because the touchbutton LED backlights bleed through around the bezel.
Mine has a small bulge near the volume keys, as the glass for the touchscreen has a little bit of a lip there on the inside that pushes the plastic bezel out a bit. Nothing I'd complain about, but putting it next to my wife's two iphones (2G and 4G), it's a step lower in build quality. And Apple doesn't let anything out that's not built perfectly. Again, this is a defect, but I don't really care to even complain about it.
Basically, if you get an HTC phone and aren't happy with the build quality, you can't be shy about returning it for a new one. It just seems that people are happier to bitch about it on the internet than actually return it for one that is built to their satisfaction. It's not like these companies don't offer support.