My Nanocube experience
I had just purchased a 24 gallon nanocube about a month ago. My first tank was (and still is) a 6 gallon eclipse.
The reason why I was interested in the 24 gal nanocube was because of the compactness. I live in a smallish dorm room (moving to a bigger one in a month) in graduate school but still wanted to have fish (2 figure 8 puffers and a molly in the nanocube and a dwarf puffer and a pygmy catfish in my 6 gal eclipse). Being a cube, it does not take up as much space as a standard long 24 gall tank. I also was attracted to the JBJ stand that is made for it (big regret, will get to later).
I liked (and still like) the eclipse and can't say I really have had any real problems with it. Being acrylic it is more prone to scratches but also much lighter (all the standard pros/cons of glass versus acrylic). The filtration system is relatively sufficient on the Eclipse but does not give you many options for filtration media. I also began to hear a lot of people say that they just take their boiwheel out because they feel it doesn't do enough good and generates tons of nitrates. Otherwise the filtration on the eclipse is decent. I like the fact that the filter design on the Eclipse is overflow proof. The lighting however is pretty insufficient. You can really only grow low light level plants. For the price, it is a good deal (find a good deal though, for God's sake, some places sell Eclipses for waaaay to much. Dr. Fosters is good).
As far as the nanocube, I was most interested in the fact that I could get a larger tank that was all in one. I have to say I like the design of the nanocube, at the very least in its uniqueness. You do lose some swimming room (volume) as the back compartment where the filter is housed probably occupies around 4 gallons, but of course you still have 24 gallons of water in your system. The back compartment is seperated into through compartments. Water flows into the first compartment from a grating and then must pass vertically through two sponges. At the bottom of that compartment is a slit where water can flow into the next compartment (chemical/biological) where the water must flow up to another slit where it runs over into the compartment where the pump pumps back into the main area of the tank. As Ron alluded to, you have to be careful with the filtration system, it can get backed up. I learned this the hard way, at least 3 times. One of which occured over a weekend that I was not in my room. I came home to the sound of a filter struggling in aerated water and water all over the floor, had seeped under the carpet under the stand, and had soaked into the stand. The JBJ stand being cheap particle board covered in some laminate expands a lot when wet (and remains so when it dries) therefore I can barely open the front door because it jams on the top of the ledge. The stand is pretty badly warped also from the water damage. I am pretty mad about that. I have a post in the DIY section about this problem regarding the pump. If you get a clog in your filters, lets say the first compartment, then your pump is going to start pumping all the water it can out of the remaining two compartments. Well that is going to lead to an extra 2-3 gallons in your main tank. Now you have a tank filled to the brim which if it hasn't already started overflowing will slowly starting trickling over the edge because the powerful flow coming out of the pump will push it over. My proposed solution was to put a float switch in the last compartment (which really doens't house anything except the pump) so that if the water level goes down too low the pump will shut off. This will prevent the pump from running dry and will also keep my floor dry.
Ron, I don't even use Carbon in my filtration. I hear that a lot of guys on here does use it either. However if you were to use it I would suggest putting it in the middle compartment. I have stuff quite a bit of media in that middle compartment (bio balls, bio bag, bag of crushed coral) and have not experienced any clogging related to that. Just don't squish them down too hard. Also did you completely wash your substrate? Also, I am not an expert but I don't think you should bother with Carbon while cycling. Carbon will probably try to absorb some of the ammonia unnecassarily which will just "wear out" the carbon.
Otherwise I really like the nanocube. The lights are definitely sufficient, as I would guess, for pretty much any planting. The pump is powerful and creates a lot of circulation in the tank (this is important, as I herad somewhere, for reefs). The only thing I don't get is, the moonlights are on the same power cord as the main lights. Granted, you are able to turn off the main lights by a button on the power supply, but if you have a timer operating your power supply (to control your main lights) then there is no way to have your moonlights automatically go/stay on when your main lights go out. Do not know how to figure this one out without some serious electrical messing around.