I've been using a Thecus 5200 with great satisfaction since autumn 2006, with 5 500GB disks, totalling a 2TB NET storage.
However as I have never had a HD fail, I can't really comment on the rebuilding of the Raid 5.
All test reports I have been reading indicate though, that the Thecus is a very reliable and fast product.
On my Gigabit Ethernet, I get transfer speeds of about 50MB/Sec, compared to the 135MB/Sec from the internal Raid 0, that is on Vista (32 and 64bit).
Setting up the Thecus was easy, all the firmware updates since the last one and a half years functioned without any problems.
The Drobo is supposed to be relatively slow in an Ethernet surrounding, according to all tests I've been reading. You can google for that.
As a backup method, I use syncronization software, which keeps my folders safe.
Hope that helps