I never ever do that.
But I have tried, in more than one occasion, given a tip after they've offered to upgrade me w/o me asking. I recall that the Sofitel in Macau was overbooked, and since I was in A-Club, they decided to upgrade me to a suite. I gave the guy 500HKD (100CAD equivalent?) and he seemed pretty pleased with it. I don't know if this is considered a bribe, but to me it isn't. Whether or not the guy at the front desk expected me to give him a tip is his issue.