I purchased an established nanocube about a week ago...contains two ocellaris, frogspawn and candy cane corals, some GSP, several different colors of zoos, a peppermint shrimp, two hermits and several ceriths and turbos. This tank had been up and running over 9 mos. with no fuge or skimmer, and everything is (as far as I can tell) in great health. Coralline growth is nearly out of control and the water quality (tested as soon as I got home) was totally pristine, without even any nitrates detectable.
It remains to be seen whether this tank will do as well in my less-experienced hands (I have other tanks available to move livestock to should it be necessary), but I'd say it has definitely flourished up to now. That's not to say fuges and skimmers aren't beneficial. I have a Euro-Reef on my 100g and wouldn't run without it. I do also plan to build a DIY skimmer for the nanocube. But, so far it appears to be in great shape without one.