SQL Server Database File Groups on a SAN: Relevant or Not?
I am not a SAN admin, but I have a very nice one in my team that takes the time to do his job proprely, and share his knowledge with us when we ask.

The way our SAN is configured makes it so there is a very large amount of cache between the SQL servers and the physical disks. In this situation, having multiple filegroups, or even splitting the DATA and LOG files on different drive letters is a moot point, as it all ends up in the same cache cluster and points to the same large array of 15000RPM disks. The cache is intelligent enough to keep the relevant stuff cached, and write to disk in a "Lazy Writer" method.

That said, althou we handle a very large amount of data, we are not overly heavy in throuput. This setup is lightning fast for our needs, and very safe between the usual backups and SAN automatic redundancy to another server room.

Sit down with your admin, tell him what your needs are, and balance the final setup with his knowledge and architecture. SAN architecture can vary greatly, so some of the "best practices" of SQL server installation may not even apply, like it did for us.