MockupScreens - UI Screen prototyping facilitation tool
http://mockupscreens.com/
I can't say how "BAD" Visio is at creating mockup screens for UI requirements and storyboarding. I'd say HTML is another approach, but having a tool to faciliate the capture, organization, and versioning of the UI mockups and storyboards would make life just that much easier.
Here's a tool that focuses soley on that part of the "fun". This can be used in ANY type of process, waterfall, Xp, etc. It's all about capturing the story and what users really want.
MockupScreens' purpose is rapid screen prototyping. So what does it do? With MockupScreens you quickly and easily create screen mockups of your application, while the coding hasn't even started yet.
MockupScreens main design goals are ease of use and productivity.
Ease of use
You just start MockupScreens and get to work. Interface is as intuitive and straight-forward as It could be. Every action can be done via keyboard shortcuts, which are consistent throughout the application. Each screen has context sensitive help, explaining in status bar the use of any action or element at all times. Screen elements and their parts are automaticaly resized and aligned to let the user focus on his goal instead of GUI design.
Productivity
With little or no experience you can draw 5 screens in 10 minutes! Each action can be invoked via keayboard. More advanced features don't clutter the interface. In addition to common screen elements (buttons, fields, lists, etc) there are "productivity" elements which you use to add and arange multiple elements at once (e.g. textfield with label, etc). Creating new screens from existing ones.
Approach
You create screens, add screen elements (buttons, text fields, grids, etc) and populate them (specify texts or data for complex elements). Screens are organized in scenarios. You then export a single screen or whole scenario to images you can use. Mockups purposefully avoid the possibility to be mistaken for the real application screens. Being "mockups", the screen elements are much simpler than screen elements from various GUI designers.