When you start looking at iSCSI versus Fibre Channel (FC), the barriers to adoption are very low for iSCSI. It really comes down to three things; cost, operational savings and existing expertise. With iSCSI, there is a lower capital investment upfront. The cost of FC switches and HBAs remains significantly higher for FC than it does for iSCSI.
A typical SMB has IT employees wearing multiple hats. Networking administrators know IP networking and they can translate that knowledge easily to support an iSCSI SAN, so you've got the existing expertise already in-house. You can gain significant operational savings because your information is moving over an IP network. It is not necessarily the same network, but it is the same type of network and that simplifies your management, training and gives you personnel transferability.
Check out the entire iSCSI SAN FAQ.