Alkyl groups have a low to zero value for F but sensible values for R.  This is most commonly explained by hyperconjugation, meaning little to no inductive effects but partial resonance effects.
CF has a much higher R/F ratio than other substituents with high degrees of conjugation.  This was studied in greater detail by Swain but is still explained best by fluoride hyperconjugation.
Positively charged substituents (i.e.,  and ) have larger positive F values due to a positive charge that is saturated near the carbon framework in question.  Negatively charged substituents (i.e., CO and SO) have much lower F values because of their ability to resonate electron density amongst the oxygen atoms and stabilize it through hydrogen-bonding with solvents.
Linear free energy relationships are still useful, despite their disadvantages when pushed to the limits.  New techniques to solve for Swain–Lupton substituent parameters involve studying chemical shifts through nuclear magnetic resonance spectroscopy.  Recently, N NMR chemical shifts and substituent effects of 1,2,3,4,5,6,7,8-octahydroacridine and derivatives were studied.  Values for R and F were found for the  group, which could not be found previously using known methods.