The Speed Triple is not a very good 2-up bike. Like previous posts, my wife is a very good sport. In the past, she'd do an out & back ride of about 1/2 hour each way. We did a couple 2 hour rides and that was pushing it. While a bit better than a full-on racer-replica, the bike still does not afford the security of a bike that is designed to hold a pillion. The pegs are absurdly wide for the pillion. In a cold climate, the high pipes offer some warmth but one must be careful of getting burned. I've also heard that if you put a low-boy pipe on the S3, you can mount Triumph Sprint pegs in the rear, which addresses the fact the stock pegs are too wide for comfort.
Discomfort for the pillion is one of the reasons I purchased a Ducati Multistrada 1200S. Now theres the best of both worlds if you're routinely going to have the sweetie onboard. Awesome power and handling with comfort for both. Now, she wouldn't even consider riding 2-up on the S3. (To top it off, she rides her own Ducati 2012 Monster 1100EVO now.)
2012 1050 Speed Triple R w/Arrow 3 to 1, Rizoma tail tidy, blinkers & frame sliders, R&G axle & engine sliders
2006 1050 Speed Triple w/Leo Vince exhaust (traded-in)
2010 Ducati Multistrada 1200S Touring w/full Termi
2004 Kawi KLX125