The capability of kinetic models to predict complex chemical systems has enormously improved in the last decades, making them an increasingly important tool for process development and optimization. Extension of these approaches to even more complex systems is hindered not only by the geometrically increasing number of reactions and species to be considered but also by the necessity of assigning accurate rate constants to all of the reactions. The recent developments in automated mechanism generators can address the tedious bookkeeping issues. The requirement for development of accurate rate constant estimates remains the job of the kineticist. This task has been aided immeasurably by the combined advances in electronic structure methods and computer performance. This article describes two areas of rate estimation. First, we discuss the development of H abstraction rate estimates from C-H bonds in alkanes, cycloalkanes, and allylic systems by H atoms and point to a surprising result found for cyclopentane. Second, we briefly review our investigation of the ethyl + O-2 reaction and demonstrate the suitability of the QRRK/MSC approach for automated mechanism generation. We conclude with some suggestions for future work in this area.