Avid Media Composer 5 is out, and it is quite an upgrade.
I won't go through the list of improvements, others have done this here, here and here.
Over at the Editblog is a cool post linking yet even more reviews and posts!

My favorite improvements are the smart tool and the AMA architecture (reviewed in the links above).

Two little (major) improvements:
The first thing I noticed when editing is that while scrubbing the timeline, the cursor kept "snapping" to the IN points.
(This can be disabled temporarily by pressing COMMAND and scrubbing or permanently as show in the pic)

Also, one thing that really bugged me in MC4 was the default "Insert" into timeline with no way to change this... It was a damn hassle with lots of back-and-forths... Now finally, there's a way to select the default behavior. Ahhhhh, relief.

This is a great upgrade by an already great product.

Congratulations to the whole AVID team for placing a lot of thought and effort into this!
:)