Installing forge from the ant script has definitely been removed. If for some reason you want to use the forge plugins, I'd download a 1.x release and try the install-forge command and use forge-1.3.2. Thanks for pointing out this out though - I'll go ahead and update the documentation.
Forge has moved on to Forge 2, and there is a SwitchYard addon for Forge 2, but I think it still needs a little work :
The Eclipse tools are definitely the more popular option for developing SwitchYard applications.
Huh. Thanks for pointing that out. I might have to take a look.
It's a pity—I really loved when I was playing around with the forge-1 a few years ago. The Eclipse tools are great, but sometimes for an outsider it can become overwhelming and hard to understand the connections between a piece of functionality and its representation in the maven project and the various XML files. (I suspect others find that a compelling reason for forge in general.) Anyway, thanks for the note.