First, I'm not an expert. I have had my 29 gallon up and running for 1 year (+4 days).
Key thing: Patience
Because of the size of the 29G (ie depth), you can actually do a mini-reef (or nano reef). I intended on only having the live rock and a clown + anemone. Anemone has long since died, and I have gone through my share of fish, and restocking and additions. I now have in it some frog spawn, pulsating xenia (which has become a forest), sea mats (zoanthids, etc), green star polyps, various mushrooms (blue FL ricordea, green stripes, and red mushrooms).
Unfortunately, a lot of my zoas have just disappeared. I think the culprit was a huge bristle worm that I didn't know about. But, that's another story.
Because of the nature of the lighting of the biocube, you can actually have a variety of corals in the 29G because the light still penetrates to the bottom.
I am going to see if I can put a picture of mine up, If I can figure out how to u/l a pic. Oh, the other inhabitants are a mandarin (I've had him for a year), and a maroon clown (since June 09)... and various clean up crew.
They seem to do well, despite my severe lack of water changes recently.