I used MC Tween all the time. When AS 3.0 came out, I loved everything about it, except the fact that there was no MC Tween. I sent an e-mail to Zeh asking if he was planning on porting it. He mentioned that he was working on a new implementation called Tweener, but that it was only for AS 2 and not yet ready for the public. Zeh was kind enough to send me the source so I spent that week porting it to AS3.
It’s funny to think back to those days, which was really not that long ago, and now I couldn’t even imagine what it would be like to make a Flash app without using Tweener!