I use mine as my main Aperture, Final Cut X and iTunes drive (in RAID 5). I specifically bought it for this reason due to the speed and size of it. I then have an old Hive RAID 5 4Tb (firewire 800) that I use as my Aperture Vault but then you could use any drive really for the vault. It's not advisable to rely on even a RAID 5 drive as your only drive because although it's pretty safe against failure, it's no safer against any potential file corruption.
I keep my iTunes backed up from the Pegasus onto my TimeCapsule as I double that up as my NAS drive for my Sonos and my original AVCHD files that I use in Final Cut X are all archived safely to Blu Ray discs. This I find works best for me and touch wood I've never lost anything.
The great thing about the R4/R6 is that it's incredibly fast (even faster than my SSD in the iMac) so means Aperture in particular flies along with no lag anywhere.
Fingers crossed, since I left it on it hasn't ejected again but Pegasus have confirmed to me that they believe there may be an iMac firmware update required and they are in talks with Apple regarding this. I do believe the drive is fine, I'm just a little nervous when connected to an iMac at the moment.