Just one way of doing things, others exist.
Workspaces are actually not shared when distributed to multiple machines, as they exist as directories in each of the multiple machines. To solve the coordination of items, any item that needs distributed from one workspace to another is copied into a central repository via SCP.
This means that sometimes I have a task which needs to wait on the items landing in the central repository. To fix this, I have the task run a shell script which polls the repository via SCP for the presence of the needed items, and it errors out if the items aren't available after five minutes.
The only downside to this is that you need to pass around a parameter (build number) to keep the builds on the same page, preventing one build from picking up a previous version built artifact. That and you have to set up a lot of SSH keys to avoid the need to pass a password in when running the SSH scripts.
Like I said, not the ideal solution, but I find it is more stable than the ssh artifact grabbing code for my particular release of Hudson (and my set of SSH servers).
One downside, the SSH servers in most Linux machines seem to really lack performance. A solution like mine tends to swamp your SSH server with a lot of connections coming in at about the same time. If you find the same happens with you, you can add timer delays (easy, imperfect solution) or you can rebuild the SSH server with high-performance patches. One day I hope that the high-performance patches make their way into the SSH server base code, provided that they don't negatively impact the SSH server security.