I was expecting a long gown, but I guess the party was more casual based on what everyone was wearing. I really like the color of Blake's dress, but I'm not thrilled with all the frou frou around the shoulders. She works it, though.
It's not the first time Gucci has used a young actress in their campaigns, and Frida Giannini seems to really like her (and I'm not sure she would be much more amenable to being told who to hire than Anna Wintour.

) From an interview earlier this year, before Blake had signed on:
http://online.wsj.com/article/SB10001424052970204792404577227510839112018.html
Blake Lively. There are lots of new actresses out there but—how can I put this?—many of them look the same. Blake is really the only one who has this sophisticated newness and attitude.
A behind the scenes video for the commercial:
http://www.youtube.com/watch?v=EmClJubkpmY
I like how she was outfitted in Gucci on the way out of Venice- and had someone else hold that big Chanel bag lol. The jacket is cool and it looks great with the men's shirt.
I don't think she'll be cutting her hair anytime soon. It gets a lot of love outside this room.

And it's very versatile - she wears it in different braids, wavy, straight, up, down and in between. But she looks really good with it up so there's no reason a shorter style wouldn't work. I can see her with a shorter, wavy Cybill Shepherd-style cut someday.