I studied these issues a lot (copyright, right of publicity, etc), and I think this particular use is fine. You are right that sometimes it is easy to figure out the text from the cloud, just like you can make out a famous photo from a very small 10x10 thumbnail, or draw Mona Lisa in 50 polygons http://rogeralsing.com/2008/12/07/genetic-programming-evolut... or as a single tweet http://www.flickr.com/photos/quasimondo/3518306770/