It still does depend on the devices. I had some onewire stuff fail due to grounding issues caused by a shared power supply. Onewire does carry the ground with it. I never looked into the root cause, but isolating the power supply solved the issue. If you are powering phone chargers, ipod chargers, etc... it will work fine.
Sure the wall warts have the UL listing. I guess what I was getting at is: so now if your ATX power supply goes "boom" & burns down your house, do you think you (or your insurance company) can sue the power supply mfg for the resulting damage? Or will they contend that it was misused (no matter how good of an electrician you are). Maybe I am just liability adverse. I tend to be much more cautious on things that are running 24/7 unattended.