Global vs user Applications Folder What is the difference between keeping applications in the global

/Applications

vs

~/Applications for a single user system on Lion?

Does the applications in the global location get extra privileges when run. I ask to decide whether it would be safe to keep downloaded unofficial applications (got outside the appstore) in the global location.
/Applications is, like you said, global.  Apps run from that folder have no different permissions or privileges if they were in any other folder.  It's the same as running an app in the ~/Downloads folder, it's just neater to have the global /Applications folder.

Having said that, apps in the ~/Applications folder are limited to being run by that user since the ~/Applications folder will have permissions on the folder for the user they're contained in.  

In my hunting around, the ~/Applications folder has global read-only access, but that can vary if a user decides to modify the ACLs (Access Control List) aka permissions.

Hope that clears it up for you!