No, yes.
Abraham posted this sample code :
<a href="http://twitter.com/share" class="twitter-share-button"
data-url="http://arst.ch/xyz" data-count="vertical"
data-via="abraham">Tweet</a>
(I think that this will post a tweet with "Tweet: http://t.co/url (via
@abraham)", although unsure)
No: this does post a t.co URL. Yes: it will redirect to your custom URL,
which will redirect the user to the final URL.
This allows you to track your clicks, but it will not allow you to post
custom URLs. You will have to keep using your previous Tweet Popup for that.
Tom
Yesterday I noticed that t.co links were unwrapped in the search, but it
looks like that is no longer the case at the moment. Probably taken
offline for a few hours to perfect the algorithm, like Twitter usually
does after implementing something new (happened to Lists too).
It looked like all t.co links are unwrapped, so don't worry ;-)
Tom