I don't think that there is a direct NEC rule against them- but you can be 'tiptoeing through a minefield' with them.
Like... does the ground pin do anything? Stick one on an old K&T box, and there still is no ground.
Basements and such will still require it to be on a GFCI.
Some places actually require receptacles to be on different circuits from lights, so that might be an issue.
As for attics, where the same fixture will both provide light AND power for servicing equipment ... meeting two code requirements with one device ... well, some AHJ's might thing that's a bit TOO clever.
