I've set it up for one customer and found it much harder to get working than FC boot, although it has worked perfectly since it was set up and now I know how to set it up would find it easier in future. The official documentation on getting it up and running is poor, although there is a very useful document posted in the documents section of the forum that does help. There is also a good guide in the partner website.
One major limitation is that you cannot use iSCSI boot when your service profiles are bound to a template as the iqn initiator value is not pooled. I will not be considering iSCSI boot for upcoming designs until this is resolved, although a change is planned I hear.
vSphere 5 is also not currently supported with iSCSI boot.
FInally there is a known issue listed in the release notes saying that the secondary iSCSI vnic cannot be used. Possibly a single point of failure concern.
So all in all, iSCSI boot is a welcome enhancement for me but still needs a bit of work to make it reay for prime time.
