I too have seen a delay. I can't quantify it, but it's long enough for me to see the heal hit my target on grid, then look to the tank to see the green number pop over his head (I've been checking for bacon heal crits).
So far it's not been a problem. Someone on the EJ forums wrote a little add-on that intercepts the information going from your comp to Blizzard's server and then back again so that you can see the tank's actual status without it making the trip. Like others have mentioned on that forum, I've actually had the experience of seeing my tank die according to my Grid but my heal hit before the info got back from Blizzard's server, effectively bringing him back to life. Very cool stuff indeed.
But, if that were the cause I wouldn't see the delay in the Bacon heal because I have that add-on. Unless it's been nuked by the expansion.
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"the people can always be brought to the bidding of the leaders. That is easy. All you have to do is tell them they are being attacked and denounce the pacifists for lack of patriotism and exposing the country to danger. It works the same way in any country."
Hermann Goering, April 1946.