I suppose if you count DOM bugs, like the memory leak, that's a problem. That's where jQuery is amazingly helpful(and presumably other libraries like it).
Considering Raphael is as slow as excanvas in IE (but much faster in other browsers), it's probably IE's fault, not excanvases.
Another JS bug in older versions of IE (6 for sure, not sure about later ones) occurs when you end an array or hash with a comma after the last element, e.g. {foo: bar,}
Also, JScript is actually surprising good and is nothing like the DOM or CSS, AFAIK the only known bugs are Named Function Expressions being parsed as Function Declarations (http://kangax.github.com/nfe/#jscript-bugs), and a couple RegExp bugs (http://blog.stevenlevithan.com/category/cross-browser).
I suppose if you count DOM bugs, like the memory leak, that's a problem. That's where jQuery is amazingly helpful(and presumably other libraries like it).
Considering Raphael is as slow as excanvas in IE (but much faster in other browsers), it's probably IE's fault, not excanvases.