I think there's a limit whereby you are saturating channels, and it would depend on your workload. I think you want to minimize head movement if you have a busy log since these are sequential writes, and there is some benefit from having those separate.

For tempdb and data files, it's more workload dependent, but ultimately I would dislike having things together for risk purposes. I don't want to lose my log and my data (and my backups) if there is a problem with the array.