Title pretty much says it all.

The canvas tag is great when what is being drawn on a page is dependent on user interaction or conditional statements.

Unfortunately there is no easy way (that I'm aware of) to generate the javascript needed for drawing inside the canvas tag. Simple shapes are easy to code by hand, but anything complex is a PITA.

There is a tremendous amount of overlap in functionality between SVG and Canvas. It would be nice if we could export/import canvas code into Inkscape, especially once Inkscape supports animation. Import might be a bit tricky I think, but serializing XML data into javascript syntax strings for export shouldn't be too hard.

Apparently this idea is being implemented in various forms elsewhere.

http://hyper-metrix.com/#Burst

http://webdev.stephband.info/canvas/convert.html

http://likethought.com/opacity/