I couldn't live without folds. Whether I'm in C++, Java, Go, Ruby, or a custom ASCII report I've written, I use them extensively. I add fold tags around every method/function implementation, and sometimes an additional one around around groups of them (e.g., classes). I generally set foldlevel to 0, so most files I enter have a few intro lines and then N folds, so that even large (1000+ lines) source files fit into a single page or two. I almost never use searches or tags to find declarations, since I can usually navigate to them directly with a single keystroke.

FWIW, I map <Space> to za, so that I can unfold/refold quickly. I also map - to zx to quickly fold up a file I may have drilled some holes in.