Just use a redirect from one version to the other and you'll have no problems. Also redirect when they don't use the www.
there's no difference but i always link to the second one with the /. the first one redirects to the / anyway so it doesnt really matter.
Sorry but Google is not smart. Their marketing department may be smart, but as a company they are quite stupid. If they were smart enough to not have a problem with this, then why did they just release the canonical tag to deal with pretty much the same issue? Or why would Google Webmaster Tools have an option to select your prefered url? It's because Google is too stupid to deal with this on their own. FREE BET: look into .htaccess redirects. You should be able to find a tutorial that shows you how to do this.