Thecus 5200 here. Been running with 5x Samsung 400GB drives for over a year now and never missed a beat.

Things to watch out for. Performance I guess. In theory those drives in RAID 5 over GigE should scream along but the CPU in the box isn't fast enough. The latest version of the box does run a lot faster. Same issue applies to all these boxes.

One thing that's a tad scary. RAID 5 is not as secure as we'd like to think it is and reliability goes down as drive size increases. I'd have thought OK, if a single drive fails no sweat, I replace the faulty drive and the RAID rebuilds itself, simple. But there's a problem.
If while that drive is being rebuild an Unrecoverable Read Error occurs at the very least that file is lost as there's no redundancy while the replacement drive is being built.
The probablility of a URE increases with drive size, yikes!
The probability of this happening is around 80% with 1TB drives from memory. As drives get bigger it approach unity, crikey this is not good.
RAID 6 attempts to address this issue but it's only a stop gap. As drive capacity increases relentlessly even it's realiability gets lower than you'd like and RAID 6 is more expensive to implement than RAID 5.
So, if you want good reliability at the moment you do better with a system that uses a larger number of smaller drives. The 2.5" ones build specifically for NAS / SAN systems yield dramatically better outcomes, at a price.
None of this may trouble you in the least. If you make regular backups to tape it is not a concern. It did catch me by surprise though, maybe ignorance is bliss. One suggestion from the storage gurus is if you run a small NAS box is to have a spare disk on hand. Most of the NAS boxes need all drives the same. When one fails in a few years it might not be possible to buy another identical drive. Keeping the spare drive spinning also sounds like good advice.

Bob.