I've had my NanoCube for about 3 months and I'm definitely pleased with it overall,, I just love the way it looks. I did make a few minor mods:
1. Removed the ceramic rings and bio-balls,,, a handful of sand has a much greater surface area for bacteria,, so why bother?
2. Added a small fan,,, tank now runs 80f pretty much constantly.
3. Upgraded the powerhead to a Maxi-Jet 1200 ,,, big mistake! ,,,way too much current. Tried a few other powerheads I had lying around and finally settled on a Maxi-Jet 400,,, seems absolutely perfect for my setup. With all the rock & sand that's in there,, there's probably only 8-9 gallons of water so I'm still getting 10x per hour turnover and it's completely silent,, unlike the rattly PHead that came with the cube. I had to cut-out a section of the black plastic divider in the filter compartment to fit the bigger powerhead.
At first I was going to tinker with the lighting, but I had a brown monti frag in there for a month and it grew just fine at the top of the tank. I think the lighting is pretty good overall, though I wouldn't attempt to keep a clam in there or anything.
My cube has a 2 inch sandbed (aragonite layer over playsand from established tank), 10lbs live rock, green open brain and some zoanthids, 7 Astrea snails, 7 zebra hermits & two beautiful juvenile Darwin Clowns.
I replace 2 gallons of water with water from my main tank every week,,, I don't dose anything directly into the cube.
I need to get more corals in here,,, my BTA has just split again so I may put one in and see how it does, though I don't expect the clowns will take to it,, you never know. If you can find them, the Darwin clowns are a great choice for these tanks as they only grow to about 3" max. and are really good looking fish.