Expert? Never heard of him. There might have been some argument against opening new browser windows or tabs in 1996 or 1999 but this is 2010. We now have faster multicore processors, RAM is cheap, and high speed internet connections are the norm.
The rule of thumb that vBulletin follows is the same one most people use on professional websites these days: Open local links in the same window and other links in a new window or tab.