I agree. IMHO, i'm a big fan of kernel developers (non directly related to ZFS), so I really prefere mdadm to hardware raid.
all hardware raid controllers has a proprietary firmware developed by each vendor, noone could know any bugs or issues that could arise and all hardware controller are much less flexible than software raid.
If you loose the hardware controller, you have to pray to be able to replace it with another, identical, one. You should use the same firmware on both controller. If the broken controller had an older firmware, there is a risk that newer firmware isn't able to load the older configuration stored on disk.
The only drawback of ZFS is ti's inability to add disks to an existent RAIDZ volume. mdadm is able to do that, I can grow an existing RAID-5/RAID-6 array by adding single disks. ZFS don't. If you want to exted a RAIDZ-2 you have to add 4 more disks.
Stupid question, as i'm new to ZFS: is the RAID-Z/Mirror configuration stored on disks like mdadm, right ? If all is gonna bad, i'll be able to move disks between servers and start them up like with mdadm ?