The page on LogP and LogD is one of the most frequently read and it has been updated to include recent publications.
Lipophilicity is possibly the most important physicochemical property of a potential drug, it plays a role in solubility, absorption, membrane penetration, plasma protein binding, distribution, CNS penetration and partitioning into other tissues or organs such as the liver and has an impact on the routes of clearance. It is important in ligand recognition, not only to the target protein but also CYP450 interactions, HERG binding, and PXR mediated enzyme induction.
The contributions of various functional groups to LogD has been explored "LogD contributions of substituents commonly used in medicinal chemistry" DOI, this study used matched molecular pairs analysis of experimental LogD values from several thousand compounds collected using the shake-flask method at pH = 7.4. They reported the average deltaLogD difference for particular molecular pairs. I've compared these experimental results with calculated LogD.