I'd agree that it has to be weighed against whether you already have a significant lens investment in the Canon system...if yes, then how much would you lose selling it all and how much would it cost to get it all back in a new mount...if no, then it just comes down to how you like the new camera.
Weigh what it is you want to get from changing cameras...what are the most important things to you - gaining speed, gaining high ISO, gaining dynamic range, better controls, larger or smaller body, more or less weight, video, stabilization, grip design, resolution, and so on. All cameras are a combination of features and compromises - pick the one that delivers the most features you desire with the least compromises that affect your photography.
Known advantages to the Sony A77 seem to be: excellent resolution and detail at low ISO, very fast shooting speed and focus speed, focus tracking ability, video performance and ability, excellent live view functionality, large electronic viewfinder, very flexible LCD panel, weatherproofed body and kit lens, built-in stabilization, live shooting histogram, multi-stacking modes built in for HDR and high ISO noise reduction, sweep panorama ability, and excellent dynamic range optimization program. Some potential compromises: some folks don't like electronic viewfinders, high ISO noise performance may not quite match the very best DSLRs on the market, battery life is average for a DSLR, about 1/2 that of the better ones on the market, files are very large and could be space hogs if you have an older computer or little memory on your harddrive, and camera buffer fills quickly when firing bursts of shots, limiting the number of frames you can take in a row to about 12 at max speed.
There's not a camera in existence that doesn't have compromises, and most have at least some stand out advantages. Whether this camera's combination of advantages and compromises best suits your needs...is up to you! It's definitely a step up in class, to the enthusiast level DSLR class - for that level of camera, it's a pretty good deal. As Kathy mentioned, availability might be spotty for a few months as they've just switched production on their Thailand factories to start making cameras at a former radio plant until they can rebuild the flooded camera plant (Sony and Nikon were both affected very hard by the Thailand floods).