It depends on your use case. In the world of preservation, ZFS is a godsend. If you're trying to run a database, copy-on-write is going to defeat you. Not that it isn't possible, but it's surely something you're going to have to work against.
Fortunately, there are types of vdevs other than RAIDZ, and using SSDs for the ZIL can improve things as well.
RAIDZ is about cheaper redundancy than mirroring; that's its optimization constraint, and by altering the ratio of drives to bit parity you can adjust to your risk taste. Since all drives need to be written and read for every read and write, the array will only be as fast as its slowest disk. But for large files, you still get the benefit of parallelism in drive bandwidth (rather than losing out from longer seeks). I see hefty throughput in video files on my home NAS, for example; over 400mb/sec locally, in practice it's limited by the gigabit Ethernet on my network.
