I've been doing more web programming lately and have been doing pretty much the same thing. These days when I visit a web site I pay attention to the design and keep an examples folder in my bookmarks that I can reference for ideas and code.
I would second some of the advice about working on a set of small bugs or features. At my current job we have 2 million+ lines of code in a proprietary language with absolutely no documentation! I found while working on smaller issues it gave me an opportunity to familiarize myself with the rest of the codebase. I also drew a diagram of the class hierarchy as I went but quickly ran out of paper. It's a daunting task but you will become familiar with the code in no time. Good luck!
For those of you who quit and then returned back to the work force, did you have any difficulty finding work or explaining the gap in employment to potential employers?