Hi,
AWPr My Spaces is a modified version of Alfresco's OOTB (out of the box) My Spaces Web script which makes AJAX calls directly to Alfresco and therefore the URLs are as you say not safe (that is most probably due to the fact that you have a cookie in your browser for accessing Alfresco URLs directly, so it's really not that unsafe.
The better way to craft download URLs though is using JSR 286 resource URLs. If you notice the What's New example Web script we provide with the AWPr release show cases just that. Regular Alfresco download URLs are proxied to resource URLs, therefore if you copy the URL and try to access it separately (and provided the JBoss portal page exposing this URL is password protected) then the user will be prompted for an authentication.
In either case it's not really a security hole but I do personally dislike exposing the Alfresco ticket to the browser as is the case with AWPr My Spaces.
Hope this helps,
–Alaaeldin