Fibre Channel technology has been around since the mid-1980s and was a ratified standard in 1994.
Fibre Channel SANs are generally more reliable than iSCSI SANs. F/C networks are in comparison to TCP/IP relatively small, this isolation reduces areas security risks and hardware failures. By combining IP and storage traffic (iSCSI) unless properly segmented could mean that your mission critical storage traffic (VMware VMotion for example) is routed next to none critical requests to facebook for example.
Another area to consider is the reliability of F/C which by its very nature delivers fixed length frames in the order they were sent with a strong level of error checking. iSCSI in comparison is delivered over TCP/IP which was designed to operate over unreliable networks which means an overhead on resubmissions and reassembly of IP packets. As I/O workloads increase, so does the amount of data that must be temporarily written to memory.
Fibre Channel performance needs to be considered against iSCSI, for a long time Ethernet has only be run at 1GB speeds. Recently 10 GB was released and has been gaining momentum. However this is new technology and still has a nice price tag associated with it.
F/C has numerous connectivity options from 1GB to 8GB fibre switches, each host requires a F/C HBA to offload the storage processing from the servers CPU. iSCSI HBAs can be either software with standard NICs or specific iSCSI HBA hardware. Should you opt for the software option then this will place overhead on the CPU of the server and the dedicated hardware HBAs are not to dissimialr in cost to F/C HBA.
So roll on FCoE....