I know of several "offices" residing in a business 1 zone that are let as residential however...
They cannot be sold as residential unless the zoning changes and it only takes a disgruntled neighbor to alert the council and you're out!
Plus, if its in a strata type situation, it may also breach the terms resulting in legal woes.
I do know of several factories that have also been converted to warehouse style apartments without proper permits but as mentioned above, the same issues would apply.
Also from what I know, local environmental issues will usually dictate how much the council may enforce the laws.
EG: Offices that have been converted to part resi that are close to an oil/gas refinery. For evacuation and OH&S reasons, it would prob be the oil company that dobs you into the council as they don't want to add to their existing public liabilities.
B.D