Are these new buttons?

http://img199.imageshack.us/img199/9479/gmailnewbuttons.png

Yes, Gmail uses CSS3 since last week

http://s3.amazonaws.com/twitpic/photos/large/78933782.png?AWSAccessKeyId=0ZRYP5X5F6FSMBCCSE82&Expires=1269861322&Signature=H%2FXPHN%2FVageasqtXUYiE16d%2FHzk%3D

was added in feb 2009
http://gmailblog.blogspot.com/2009/02/new-ways-to-label-with-move-to-and-auto.html

hebbet I think the OP was referring to the rounded corners

Yes, I think the buttons with the round corners are new.