SPO made it's 1st update statement in October 2011 which allows BCS (web services) on SharePoint Online. This is the 2nd change to the SP2010 online version (Feb 2012),
Ability to scale up to 500K users was 20k.
Site Collection Recycle Bin - ability to self restore includes a full site collection restore.
Ability to invite non-domain users - Simplifies Collaboration with partners, customers, etc as they can use their own email adrs.
Changes to how your browser handles to PDF files - use to have to download and then open the pdf document. Now will open pdf reader once clicked.