Just an observation here, but I was one of the people here that was seeing failures every 10-14 days depending on load. About 7 weeks ago, I converted some of my volumes to iSCSI and downloaded an iSCSI initiator for my Mac clients. Since converting the Time Machine targets, I have yet to have a failure. I know that there have been failures reported that do not involve Time Machine; I think I may have posted one myself. Still, my system has been stable for longer than it has been since purchase over a year ago. I realize that iSCSI isn't for everyone, but for any clients that are hard wired with Gigabit Ethernet, it might at least buy you some stability. The downside to testing this is that iSCSI for Mac is pay-for-play. The GlobalSan Initiator I am using set me back $90.00 US, but so far has been worth it. I don't have any hard data, but overall file transfer performance to and from the iSCSI/block volumes seems better overall.
Note that I am still using AFP for shares, and I also stared using CIFS for Windows clients on my network - these are still primarily accessed via the wireless network. I haven't been moving large amounts of on the share for a while now, so again, this evidence is anecdotal at best. But anything that helps users with this problem is worth exploring IMO. As disk prices come down, I may start moving to new drives if/when I do have another failure.
In theory, it would probably be best to abandon RAID-5 moving forward. Having all the failures I've experienced, I've realized that the rebuild times are so long on the 2TB drives that I really am setting myself up for catastrophic failure (2 drives). If I keep my current ReadyNAS, I might do RAID-10; if I step up to another NAS, I may suck it up and go for more drives to do RAID-6.
Hope this helps someone!