Since the availability of Office 365 and SharePoint 2010 Online, this was a frequent request from customer to get usage statistics.
Unfortunately, until few days, these statistics were not available.
Few days the SharePoint Online product group has introduced new features (see http://blog.hametbenoit.info/Lists/Posts/Post.aspx?ID=309), but it seems they don’t communicate on this one.
From now, usage analytics is now available on SharePoint Online BUT you can’t see it on the SharePoint Administration Portal neither from the Site Settings, as you can with SharePoint On Premises.
Moreover, the statistics provided are ONLY showing data, there is no chart like with SharePoint On Premise.
To access the statistics, you have to go the usagedetails.aspx page (/_layouts/usageDetails.aspx). This is available on both Public and Private site collections.