With all the chatter comparing the merits of Fibre Channel vs. iSCSI SANs, it's worthwhile to remember that the two are not mutually exclusive.
As Jay Kramer of iStor Networks points out in this article, iSCSI can provide an inexpensive adjunct to existing FC networks. Mixing the two together, in fact, may become the preferred method for introducing virtualized server and storage networks.
Once you've decided to introduce a protocol-independent SAN topology, the trick is to find the most efficient and least costly way of extending it to, say, distributed locations and departmental systems. If many of these networks are using low-end commodity storage and servers, then an IP SAN is probably the way to go.
And now that IP SANs are capable of handling mission-critical applications like e-mail, ecommerce and now cluster and grid computing, there's really not much that Fibre Channel can handle that iSCSI can't.
Small businesses, of course, are probably going to go iSCSI from the ground up as a matter of simple economics. But even large FC users should explore iSCSI where it makes sense. And perhaps today's small iSCSI enterprise may find the need to fold in some Fibre Channel someday.