I made a small one with a flower pot covered by a bucket. I put food in, it disappears. Seems to be working.

I'm hoping to implement the technique shown in the video in the grow beds I'm gonna build in my new greenhouse. I'm just not sure which species would better suit my needs. I can't think of any place to get nightcrawlers in my area which would pose a problem for that possibility. And then if the books are right and RWs like to stay on the surface, I don't think it would work the way I want.

The dimensions I've been thinking of for my grow beds are 3 feet high, 6 or 4 feet long, and 3 feet wide.

Probably depends on your climate. As I recall, that video about the worm tower is from Australia.

Before I started my worm pit, I created about 4 cone-shaped structures of horse manure, soil,compost and populated the cone with the compost worms found in the horse manure. I fed the worms blended up kitchen scraps buried within the cone. The compost worm population exploded. At some point, I decided to move my 'cones' into one location and that is the begining of my worm pits ... the surface of which is one solid red squirm. All this from the worms found in aged horse manure.

Interesting. Is there any evidence that the worms actually crawl out into the surrounding soil and distribute their castings? I'm somehow dubious that that composting worms, who naturally reside in forest litter, are going to burrow through soil just to take a dump.

Supposedly normal earthworms get involved and distribute the castings.

I've tried this with without the pipes or pots...just a mini in-ground worm "hole". The red worms don't burrow into the earth, but they do continue to produce castings. Eventually roots from the surrounding plants get into the worm hole. Next time I'll probably use pots riddled with holes.

The graphic in that video with the worms wandering out into the garden soil is unrealistic...JMO. But the concept of getting composting worms working directly in the garden is very practical. I just don't know if it's simpler to have a bunch of worm towers all over the garden (they need to be fed & watered) or just a good worm bin system from which you harvest and deploy vermicompost.

I hesitated to comment on this, because I am a very, very new gardener. I tried this with mixed results. I put in four of these, very much like the video says. Here is a link photo of three of them back in the spring. I made mine taller, so I wouldn't have to bend over to feed them.
http://vermicomposters.ning.com/photo/garden-2010-3?context=user

Initially, the tomato plants around the towers were the ones that wilted first. And in the very back bed, I feared that the ants in the neighbor's yard that I had been battling all year were the ones eating the food, and there were no worms, so I stopped feeding it. The one you can't see was near a rhubarb plant and the plant died. I am not sure why, and I can't say it was because of the tower at all, since, as I say, I am a very new gardener. But the one near the cucumber plants is just crawling with worms, and my cukes are very abundant. The soil there was not great, and it seems good now, though I have used lots of other amendments, not just the tower by any means.
I use the tower that is by the dead rhubarb now for kitty poo, since there are no edible plants there, and I figure it is as good a way as any.

So, my recommendation would be to make sure there are no large ant colonies around first when locating your tower, don't put it RIGHT in your garden, or super near your plants, just use it as a general soil builder. And it makes a nice place for small amounts of animal poop if located away from edible plants.