Shared history in zsh is essential to my workflow. I also keep many terminals open, and while I do separate them by task, I often just pick one which happens to be in the right directory and start typing away. I always search through history using Ctrl-R, and almost never use up-arrow cycling. Shared history makes this work seamlessly.

This is obviously configurable, so if you prefer a different workflow, zsh will accomodate it.