I noticed in one of my previous posts, a comment on the fact that because SANs typically fragment their data physically over multiple disks, then they are "fragmented by design" and hence do not benefit from being defragmented.
Unfortunately the author of that post does not understand the difference between defragging the SAN and defragging the NTFS volume on the SAN.
In simple terms, if NTFS is fragmented, Windows has to issue more I/O requests (spilt I/O etc). These I/O requests added up very quickly and slow the overall performance of the OS and the SAN. In this scenario, it is Windows perception of the disk that matters. It spends a significant amount of time blocking and waiting on I/Os that just aren't required.
At the end of the day, the evidence also points to the fact that defragging makes a difference. Time and time again the results are the same. The clock does not lie.
If your SAN administrators tell you otherwise, then ask them to do a test... but be careful some people don't like to be proven wrong.
If it's your Domino server... give Defrag.NSF a try.