The major problem I see with the new retweet feature in beta on Twitter is that (for now) the posts are invisible to API clients. Since I do most of my Twitter activity through Twidroid (on my phone) and Twhirl (on the desktop), that means if someone I follow retweets a post using the new feature on the website, I won’t see it.
Update (Nov. 20): That was fast! Twidroid has released a new version that supports the native retweet capability, so now I can see them on my phone. It also lets you choose whether to retweet the classic way (open a post pre-filled with the original, so that you can edit it) or natively. If you use the native version and have multiple accounts, Twidroid Pro is smart enough to use the one that’s following the original poster. I haven’t quite figured out how it decides which account to use when retweeting someone you don’t follow, though.