Agreed I have had lots of performance problems with the canvas tag trying to simple things that ran blazingly fast in flash. HTML 5 (buzz) has a long way to go before it can really compete with flash. Similar demo running in flash.
http://www.flash-filter.net/rain-drop-water-effect.phtml
Same here. I built an isometric strategy game in canvas but had to abandon it because I couldn't get over 12 fps on firefox on a reasonably resolution.