Durability is a big downside. Mice, skunks and other rodents can do a lot of damage, not to mention abuse by the beekeeper. They are impossible to repair unlike wood and you still do need to paint them to protect them from UV light.

They do provide some insulation which may be benifical in the far north and are lighter weight. I've read reports that even in more moderate climates they will start brooding up faster in the spring because they can keep more space warm.

Beesource is a large and very active forum. There are also a few active mailing lists (Bee-L is probably the largest I know of.)

Here is a link that might be useful: Beesource Forum