For the average user I Highly recommend using Ext3 everybody else has already expounded its advantages. However, I will sum them up again: Reliability, Ease of use, Standardization, Performance(yes it really does perform well even in really weird situations).
In recent machines the only time I have deviated from that was for a buddy who wanted a machine to copy all of movies, dvds, tv shows, and music onto, and wanted to download more. He showed up with 3 1TB Hard drives and said make it work, make it easy and make it reliable.
So here I used ZFS, because I know the issues of using ubuntu (his distro of choice) and software raids in the long run. I felt that if an upgrade went wrong he would be able to recover on his own, and it would not leave a system that I could remote into. Data integrity is not as guaranteed. The last reason was Disk sizes, if he has a problem will he be able to get another 1 TB disk, will they still be expensive, maybe it will happen so far in the future he will not be able to reliably find disk so small, if he just wants to upgrade.
I used ZFS with copies set to 2, and compression on max. This way if he loses a drive hes fine, whatever isn't small will be compressed (he doesn't need speed, he is what TV and listening to music).
The drawbacks, I had to write a custom script to guarantee that ubuntu always mounted the disks/zfs pool properly. If I am not around where will he get help? What if something fails in an unexpected way?
That is where I am at on all single or dual disk systems I am using Ext3 on more than that I am using either raid5+Ext3 or ZFS.