My company, Crawdad Technologies, sells software which does text analysis. Here is a picture of the semantic network that represents Genesis, Chapters 1-3--basically from the beginning of the universe until Adam and Eve got thrown out of paradise, and before all the "begating" began... The technology uses natural language processing to identify words and the parts of speech (remember diagramming sentences in grade school?) and then renders a network visualization. The most "important" words are shown as a network (red=most most important, yellow=2nd, plain=3rd) and the connections represent semantic connections by the author.
The network represents the "mental map" that the average reader gets after reading the text.
If you happen to be a qualitative data researcher (either as an academic, student, or market researcher), I do have to put in a mini-pitch and say we have the best computerized text analysis software available... and you can try for 30 days free! Go to http:://www.crawdadtech.com .
If you want to see our text analysis engine in a more practical setting, visit wonkosphere.com, which is using the technology to track over 1200 political blogs as they buzz on the U.S. presidential elections.