Been reading some of the T-Bird reviews in the press and an ongoing theme in most is that Triumph hopes to woo HD people to the it's bikes.
Personally, I don't think this will happen to any great degree. There will be some that have a soft spot for Triumphs and are not into the rest of the HD experience that might make the switch (probably mostly older riders like myself). I really liked my HD, but had already decided I wanted a Triumph again, and the '09 America drew me to it.
However, a lot of HD riders are into the brand for the social aspect as well as the riding and HD ownership aspects. Almost every dealer has a HOG chapter, and they stay pretty busy with local social and charity events, many of which are family orientated. Then there is a state rally every year plus a annual National one. All very well supported by HD. And since all HD bikes are of the same basic type, the owners start right off with a lot more in common together. Yes, Sportsters and V-Rods do get teased some, but their owners are still generally accepted as HD riders.
Due to work conflicts, and being more of a loner type, I wasn't as active while I was HOG member, but I still enjoyed my time with them. They do make you feel a part of a bigger something, a ready made group of friends.I met lots of members who would never give that up.
Triumph's diverse range of bikes, and their seemingly lack of serious support, makes it a bit more difficult for owners to feel a part of something social. In my local RAT group, I think I'm the only local cruiser owner. There are a couple of others, I think, but they only get with the group once in a great while. Most other members are into either the street fighter bikes, the modern Classics or older Trumpets.
When I stop at my local HD dealer once a month or so, to pick up the free MC publications, I feel more in common with the sales people I know there and the HOG members I run into that remember than I do when I visit my multi brand Triumph dealer (I keep trying to talk the dealership manager into becoming a Triumph dealer, as well

)
I think the T-Bird will do very well, but I think it will be people who were inclined to buy a Jap V-twin who will be more drawn to it. I think it will take more than just a bike, no matter how good, to win over more HD people.