To me this is big news even though it looks like it has been there for a few months. I didn't check with Sun, but I assume that since this library is hosted in a repository in the java.net domain, that it is officially ok with them to be the ones providing it through their repository:
http://download.java.net/maven/2/javax/transaction/jta/1.0.1B/

I happened to see this as a comment on someone's blog. Might be good to check into, as it would save a lot of people the headache of installing jta manually.

Ditto for java-mail (if that jar is also hosted there, I think it probably is but didn't check).