Actually, RAID 5 is the only unusable one, the one businesses stay *away* from :)"
You get the worst of both worlds, crappiest performance and some loss of disk space (although the wasted space becomes less proportionally with more disks).
If you want redundancy, you use RAID 1, if you want speed you use RAID 0, if you want speed and redundancy you use RAID 1+0 (which is an awful lot of disks).
RAID 5 is the red headed step child which you can use for archive storage systems (where performance isn't critical), but thats about it.