I had one snowflake before when my tank was set up as a fowlr tank and yea, they are really cool. I also agree that there should only be one per tank and they do get very very big. I thought the minimum size tank was around 75 gallons or more, but not completely sure on that.
These eels are also very blind and so mine would tend to attack any fish I had in with it, even my porcupine puffer and my lionfish. They will however, eat small fish, snails, clams, and other inverts as well so it is best to keep them either in a tank with big, fast fish, or feed them very often so that they dont need to scavange for any food.
The other issue I found and was pointed out is that they are really really good at getting out of a tank and can fit in the smallest little hole it seems. Mine got out of the main tank and into the overflow once and I had ducktaped the glass tops to the tank in the back.
One other thing, they are going to be in and out of any live rock you have and will actually dig a tunnel underneath a rock or two in order to hide out during the day time. This means that you have to have well stacked rock work or glue them together. I also suggest making a layer of base rock that is touching the glass on the bottom of the tank so that they cant dig under it and cause it to shift and crush them. When they get real big, I would think that any rock stacking wouldnt be strong enough so I would either find some really good glue or just have the rock spread out on the bottom of the tank. Even if you dont care if the eel gets crushed or stuck under a rock, you will if a rock tumbles and breaks the glass of your tank! They are also apt to get into any intakes or powerhead nozzles. Mine loved trying to get into my powerheads but luckily I have all mine plumbed underneatht the tank and am pushing out 1200 gallons per hour so he couldnt really fight the current coming out of them.
Here is a little compilation of videos of my Snowflake Moray Eel if you want to check it out. This one is pretty small actually, about 10 inches long and around the width of a dime or so. It is always best to buy them around this size since smaller ones are more sensitive and easily stressed while bigger ones are more set in their ways and may cause havoc to the other fish in your tank. Also, make sure you ask to see the LFS feed it to make sure that it is eating since they are sometimes not willing to eat and starve which it is in your best interest to not bring them home.
http://s96.photobucket.com/albums/l162/tommygunnz76/?action=view¤t=MyS.flv