They certainly dont sell as well now that everyone and their mother is publishing an ebook on one topic or another... not like, say, they did a year ago or more.
That said, the value is in the results in my opinion.
Since you can easily get an instant refund on almost any ebook purchase you make, there isnt very much risk involved in finding out whether the information is worth the price they are asking or not.
Personally, I find the info products extremely valuable. Of course, I'm choosy about what I purchase, and only buy the products that I am sincerely interested in or need at that time. And I especially like constantly-updated products, such as the SEO Ebook by Aaron Wall.
For products like that, $50 or $100 is a drop in the bucket compared to what you can earn once you apply the information.