From Idea Digital Imaging:
PSLogSearch has been designed to quickly search your Photoshop History Log, but can be used to search any log or text file. It requires Adobe Photoshop CS or CS2 because previous versions of Photoshop do not offer a log feature.
To use it, launch it and then help it locate you log file - normally located in your Documents folder.
Enter search terms separated by spaces in the search box and hit enter or return. The terms are treated as being cumulative which means that the results contain all of the terms that you've typed.
You can add context to the search results by choosing the number of lines after, before or both before and after your search hits.