Traditional brainstorming works because multiple people give their ideas of a specific topic which sparks more ideas from the other brainstormers. For example if we are brainstorming "Types of Animals" and you say "dog" I might think of a "wolf" or other similar animal to add to the brainstorm. This is the same way a mind map works with a single person. Putting your thoughts into a mind map allows you to see them visually and associate them withnew ideas. Use the map structure in XMind to create a branstorm and use shortcuts so you can snap new topics into place without loosing your train of thought. Remember that you can use the Enter key to create new main topics and the Tab key to create subtopics.
Here is 20 minutes of brainstorming with XMind.
Planning a Website
Using mind maps for the planning process of a website's construction in extremely useful for totally different reasons than it is for brainstorming. Instead of inspiring new ideas and topics, which might happen anyway, the power of mind mapping your website plans comes from the clearer thinking you get with everything in front of you. Using mind maps allows web designers to create both a plan for themselves and their client. Most clients enjoy getting a colorful presentation on paper describing the site plans, progress, etc. Now we can see the brainstorm built on and now we have the basics of a website plan. It is surely easier to divide up tasks for this project after looking at the mind map rather than a wordy outline.