Over 99 % of all tables I see in my daily work is heap tables. Tom Kyte would probably claim that in many circumstances this would be a design error. For instance is the use of IOTs (index organized tables) strongly underestimated. The main reason for this is probably that most DBAs have little or no knowledge or experience with these kind of tables. Jonathan Lewis presented a link to the following article series in his Oracle blog. If you don´t have any IOTs in your database you should probaly take your time reading these articles.