Web AIM (http://www.webaim.org/) conducted a survey of screen reader use last year and they have followed it up this year with another one. The survey sample is small, self selected and probably biased towards more experienced screen reader users based in North America.
Even when this is born in mind the results of the two surveys make interesting reading. JAWS is still the leading screen reader by a long way but compared to last year the free screen readers such as NVDA show a steep rise in use although often not as the primary screen reader. Also around half of the latest survey considered the free screen readers to be a viable alternative to JAWS. It is taking time to chip away at an established near monopoly but these surveys hint that change is on the way.
For anyone interested in assistive technology or accessiblity issues it is worth reading both the original survey and the latest results.
Peter Cheer
Assistive Technology Trainer
Kenya Society for the Blind
Nairobi