As it is widgets have created quite a stir, I feel the next step is Canvas. Looking at the preview I am very excited even though I have not yet tried it. Looks like it is going to take customization to a new level and at the same time making it as easy as possible.
And some prediction and hope: given that one among two last wishes one can have from wordpress.com would be to change the layout (other one to execute java script/php code in posts/pages). The reason why guys at wp.com have still not given that ability to end users may be that they do not want users to dirty their hands hand coding things or to mess up things. In that sense, canvas will be just what can be offered : easy to use but still not giving complete control. Just like their widgets.
Infacts, canvas is what I like to call – widgets on steriods 🙂