Actually, you can! But, by default they are marked hidden. If you want to see your friends' +1's they will need to mark them visible for their Google accounts.
You can do this at https://profiles.google.com/
Once they have them marked to "show this tab on my profile" it will appear there. To visit that page go to the url https://profiles.google.com/USERNAME/plusones and just change the USERNAME to their Google username. For example mine would be https://profiles.google.com/groovedexter/plusones.
Hope that helps!