Here is an extremely interesting blog post from Ken Varnum on the RSSLib blog entitled “FeedVis: An RSS Tag Cloud on Steroids” [http://www.rss4lib.com/2008/12/feedvis_an_rss_tag_cloud_on_st.html]:
“FeedVis is a word cloud/feed visualization tool. Give it a bunch of RSS feeds (inOPML), it will digest them for you, and present a word frequency chart which you can interact with by selecting date ranges, specific blogs, or both.
I selected about 75 RSS- and library-related feeds and generated an OPML file, which I then uploaded to FeedVis. This is what the interface looks like. Across the top is a time scale — a yellow bar indicates each day in the 30-day window, with the number of posts for each day shown. Beneath that is a word cloud, showing the most common words in the collection of feeds for the selected time period (in this case, all feeds for all 30 days).
If you select a single blog, FeedVis focuses on that blog and redraws the word cloud for you with a slick AJAX effect. The size of the word shows frequency (per thousand words), as you’d expect. The color indicates recent shifts in popularity. If a word has been used more in the selected time period than overall, it shows up as green. If a word has been used less frequently in the selected time period than overall, it’s red.
You can interact with this data yourself at http://jasonpriem.com/feedvis/index.php?account=varnum. Of course, you can also create your own by exporting an OPML file from your favorite RSS reader (no more than 100 feeds can be imported at once, however).”