[JKT]

There currently isn't a "Create new Workspace from open/selected tabs" feature. There are two ways you can get around this:

1. Select all tabs in the drawer you want to be in the new Workspace (command-click to make discontinuous selections) and either Command-X to cut them or Command-C to copy them. Create a new Workspace, click in the drawer to give it focus and then paste to load the tabs you cut/copied from the prior Workspace. Take your snapshot to preserve the new Workspace.

2. Open the Workspace manager and rename your current Workspace. Create a new Default Workspace to replace it. [Edit - I forgot to say that you should take a snapshot of the Workspace to preserve its state between sessions]

Edit: Hopefully, OmniWeb 6 will offer a better interface for managing Workspaces which will allow you to e.g. create Workspaces from selections, copy or move individual tabs from one Workspace to another in the Manager window, etc.