There are 2 problems here, a technical one and a legal one.

I'm not sure about Windows 8, but for Windows 7, the situation is:

Technically, yes, there are many workarounds to do the trick.

Legally, it depends

if you do have a existing license of a prior version of Windows assigned to the device, then yes, you can do a clean install using those workarounds, legally.

if you do not, then you can't, even if you do a fake 'upgrade' by 'install a trial/evaluation first' (basically as the 'double install' workaround), or "stick in an old dvd and dump the files", if your license of the old dvd has been assigned to another device, then you are still violating the 'upgrade' license, even if you installed and activated Windows 8 successfully.

BTW, Paul Thurrot discussed this problem in yesterday's Windows Weekly, and he promised to investigate this more as soon as possible.