Tim Grey is responsible for accelerating my grasp of Photoshop. He does a good job of identifying common issues that people have with photo processing in Adobe’s applications and writing well thought out answers to address the problems. His Digital Darkroom Quarterly (now called Pixology) and his Ask Tim Grey newsletter provide easy to understand answers to questions you might not have even thought to ask.
Tim is an expert in Photoshop and Lightroom, with extremely good access to Adobe for questions that involve “why does this Photoshop filter work this way?” He is also a published author, with several books on color management and digital darkroom workflow, including both Photoshop and Lightroom workflows.