I use focus follows mouse and it works pretty great. There are a few circumstances where Openbox's focus follows mouse mode is more finely tuned (for instance, when un-maximizing a window, the window under the cursor receives focus instead of keeping it on the window that you just unmaximized); overall it works really well.

One thing the gnome3 guys are doing is putting application menu stuff up in the task bar (window-specific menus will remain in the app window), but when focus-follows-mouse is enabled, the app-menu will remain in the menu-bar instead of up in the panel.