Tibor Karaszi argues that index fragmentation is a less serious issue than most DBAs think:
You know the story. Every week or so, we defragment the indexes. Many of us uses Ola Hallengren’s great script for this, some uses Maintenance Plans, and there are of course other alternatives as well. But are we just wasting time and effort? Quite probably we are. I’m going to start with some basics, and then do some reasoning, and finally give you some numbers of a very simple test that I ran. The T-SQL code is available. If you give it a try, please let us know your finding for your environment by adding a comment. I will do some generalizations and simplifications, to avid this post being 10 times longer.
Jeff Moden has a couple of great talks on the topic which really pushed me in this direction. Grab his slides from the SQL Saturday site for a much deeper look at this topic.