Bottom line: People can analyze, compare and identify information 25-50% faster using treemaps versus tables; people prefer treemaps to tables in subjective ratings including ease-of-use, clarity, and usefulness; and people can learn to use treemaps quickly without any training.
Treemaps are faster
Users were timed to complete several types of tasks. In every instance users completed the task faster with a treemap.

Users prefer treemaps
When asked to rate each interface on a scale from 1 to 7, treemaps rated higher in every category.