>Is it preferable to create a clustered index on every table?

You want to create indexes because this helps performance. Every time you do a query, you don't wnat to do a table scan. If your tables get to be mdeium to large in size, you'll be there a long time.

Clustered indexes should be done on the field/expression that is used the most for your queries. The object of the game in SQL Server is to return the least number of pages in a query. Clustered indexes help with this because clustered indexes dictate the physical order of your rows in the tabe. If your queries return a relatively small subset of data, a clustered index could really help.