Matt,
The reason I prefer a drive pool technology is because I don't like the downsides that come with RAID. I've used RAID in the past so I know what they mean. Ok, so RAID offers me the option of speeding things up a bit. Is that important to me, as a home user? No. This is simply data storage. If I wanted to speed things up, I'll put the server OS on an SSD, but harddisks are mainly storage for streaming/archiving pursposes. I don't need raw speed for that. About every harddisk nowadays offers about 100 MB/s or more which is more than sufficient, especially if you consider the maximum theoretical speed Gigabit ethernet offers (125 MB/s, which is never reached).
Just FYI: I've put Cat7 cable throughout my entire house so I could easily upgrade to 10 gigabit network speeds if I wanted to but I'll wait just a little bit longer until the prices of the necessary switches reach 'consumer levels'. Maybe then it would make sense to use RAID again for speed reasons, but on the other hand it would still not be necessary for the use I'm having for this server (streaming/archiving). Not even HD streaming requires that much amount of bandwidth.
RAID is also not very flexible when it comes to expanding the arrays. For one, you need every disk in the array to be the same size, type and preferably brand. This means if you use RAID5, with a minimum of three disks, and you want to increase the storage capacity, you'll need to buy at least three new disks, AND most likely you'll scrap the three you had because you'll have no more use for them. That is wasteful and a shame.
Not to mention that, if you upgrade an array by pulling a disk from it and upgrading it with a larger one, then having the array rebuild itself and repeating this until you've done all the disk in the array takes A LOT of time. Probably days! I don't have that much patience!
unRAID is different when it comes to this, but I've read it also takes a lot of time to rebuild an array when it was compromised. Don't need that, don't want that.
What can be simpler than the way WHS did it? You want more storage? Pop in a new drive run the wizard and 30 seconds later the capacity of the drive is added to the pool. ALL of it! You want certain folders to be protected against drive failure because they hold important data? No problem: just select those folders and they'll be duplicated on different disks.
The only thing WHS lacked in my opinion was a decent backup facility. Sort of like doing an rsync to a second WHS. That would have been awesome.
I've never tried OpenFiler to be honest, so I can't comment on their GUI. It was on my to-do list, but I never got around to it. I did use FreeNAS before, but that was back in the 6.x days. It wasn't bad, but it clearly needed a bit more work. It was one of the main reasons I went with WHS in the end. Also -to be honest- because I couldn't be bothered anymore to tinker with it a lot at that time. Our son was born in that period, and spare time grew short... so I went with a MS solution.
Now, with regards to FreeNAS again... it seems that Olivier Cochard-Labbe, the original creator of FreeNAS stopped developing it and handed it over to IXSystems who have done a complete rewrite. The 8.x betas are the first results of this new code fork and it seems to come with a new GUI as well! I haven't used it yet though, will probably wait until the first reviews... but I AM curious to learn more about ZFS!
