Based on the instrucions in this article
, i have extended my
Sitefinity\Admin\ControlTemplates\Pages\PagePropertiesEdit.ascx.cs witch does the admin ui for page editing.
Basically, i intercept Page Edit, look for the (GUID)PageId, and use it for displaying/storing/loading the data of my custom attribute controls to my database.
Also, for accessing the attributes in your template or usercontrol, you have to use the PageId and load the data from your database.
from Ivan Dimitrov in http://www.sitefinity.com/support/forums/sitefinity-3-x/developing-with-sitefinity/extend-page-properties.aspx#737547
"This functionality will be available after Sitefinity 4.0, which will be
released this year."