I posed this question too a while back, and got some useful responses. http://www.canonrumors.com/forum/index.php/topic,1184.msg16117.html#msg16117
Blower idea is great for keeping the lens clear of large droplets.
I used the Op/Tech rain cover on my 7D (upgraded to this since my post) - it was OK. Sort of did the job - there's an opening on the rear end of the cover which is supposed to stay on the camera once you have the eyepiece clipped in place over it. Unfortunately, my eyepiece would not 'click' in place, kept falling off, and thus it all become somewhat annoying. Actually, it was more than annoying. As a last resort (I was already in the midst of the water spray), I decided not to clip the rear opening of the cover under the eyepiece, i.e. I ended up with a small mobile unsealed opening in the rear cover and a few drops of water got to the outside of the camera body. Low and behold, I had an error message on my 7D for over an hour after that. It's been fine for the past 2-3 weeks since - guess it dried out!
So if you want to use the Op/Tech, make sure you spend more time than I did tweaking it and making sure it fits under the eyepiece and the latter clicks in place.
Maybe the trash bag would be better after all!