I just saw a show on This Old House this week that didn't use tongue-and-groove but the wood they used was touted to last longer than the homeowner. (Check your local listings for the show 'number' and go to This Old House's Home Page and see if you can get more info. Maybe someone has the info from the Forum.)
The installer (Bob DeSilva) used an adhesive to hold the planks to the joists, then he 'tacked' the strips. The adhesive, in concert with the tacks, keeps the planks in place. I'm sorry I wasn't paying too much attention to the TV that night. This particular type of installation is better for exposed porches since rain and snow are easily 'drained' off the porch's surface. If your porch is exposed, it's worth considering. T&G flooring, outside, will not drain moisture as well as strips/planks because they're 'joined'.