Spyros,
You can create 2 fields, one where users enter the % complete as numeric value and second one with formula (calculated) that will transform this into % and use this field for display on all views.
Hope this will work for you.
Best regards,
Anton Kravtsov
www.projectserverblog.com
Anton Kravtsov MCTS Project Server 2010 | www.ProjectServerBlog.com