It's good that you're looking for feedback because that's all that I can offer. Though we haven't used them yet, you may find my research interesing. I've been looking into getting a new server for my work as well and here's what I've found regarding these drives. Mind you, I've ultimately come back around to them, but not for the reasons I initially thought.
First, the Constellation ES drives are some of the first nearline SAS drives available so this is new to a lot of people. A lot of forums say that nearline drives are just a marketing gimmick and are really just SATA drives with a different interface, but that doesn't seem to be quite right. They still have better reliability and are actually meant for 24/7 runtime. However, they are not meant for the kind of abuse a heavy database would put them through, which is why the other SAS drives are still going to be produced. These are meant basically for light to normal server use and backup purposes.
Here's a link that might help outline the benefits of nearline SAS over SATA
We're going to be using these in a small file/exchange server running Small Business Server 2011 for about 10-15 users. Though if you're going to be separating these drives into that small of arrays, you must be expecting a very heavy workload on the servers, in which case, these may not do it for you.
And for reference, I don't do this for a living, but aside from this research for my work, computers and servers are a very big hobby of mine.
Good luck!
