Rustle,
When I last checked, operating VFR also was operating to
rules. However, when you look at the rules for operating Class G/VMC, the differences betwen IFR and VFR are very subtle - with the most dramatic difference probably being that quadrantals and flight levels are recommended VFR best practice vs. IFR requirements.
Obviously when operating in IMC there is the fundamental difference that you can not possibly be flying VFR
.