It is very easy to enable public collaboration on a SpreadsheetLIVE document but please remember that a publicly enabled document can be viewed by an user of SpreadsheetLIVE so make sure that the spreadsheet does not contain any sensitive information that you would not want other people to see.
To enable public collaboration on a SpreadsheetLIVE document you need to select the spreadsheet document from your workspace and then use the right-mouse click button to access the content menu (as shown in the image below) and select Manage Sharing > Make Public.
On the Publicize Workbook dialog you can decide whether you would like to grant public users Read or Write permissions to the document. Public collaborators will be able to receive real-time updates regardless of their access level but they will require Write permissions if you would like them to be able to add to or modify the document. Once you have made the appropriate selections remember to click Yes to apply the changes!
At this point your document is publicly accessible (you will notice that the icon beside the document has changed to indicate that the document is now a public document). SpreadsheetLIVE user can now find your public document through the Workbook Menu > Public link on their workspace page.
How to make your SpreadsheetLIVE user account publicly accessible
If you wish to make use of the collaboration feature of SpreadsheetLIVE you will need to ensure that your user account is publicly accessible.
In order to do this you will need to select the MyAccount link from your SpreadsheetLIVE home page.
Under the Change Account Details section you will see a checkbox that says I want my profile to be public. Ensure that you have placed a check beside this option and then click Save Account Details.
At this point your SpreadsheetLIVE user account will be publicly accessible and other users will be able to invite you to collaborate on documents with them.