In the Featured news there is this article:- https://community.secondlife.com/blogs/entry/2577-important-changes-to-your-second-life-account-introducing-tilia/ which in brief announces that from 1st August your USD transactions are to be handled by Tilia, a specially created subsidiary. All the details are in the article.
A problem for some will be to provide identification required in order to process credit. I'm not a US citizen so I'd have to obtain a passport just for this purpose. I
THE TL;DR VERSION OF ALL OF THE ABOVE
The purpose of this thread is to provide a quick summary for newcomers of the information regarding Tilia that we currently have available to us.
I've edited and updated it a bit to reflect a few new things that LL has clarified since I originally posted it. It has been effectively superseded by the longer and more detailed FAQ OP on the Official Tilia Q&A Forum Thread, posted by LL itself, but it is possible that some may still want a shorter