Yes, indeed. I find it very satisfying to acknowledge a job well done, in that it costs me nothing but can brighten the person's day considerably (I assume, just going by how much I appreciate genuine recognition of unacknowledged hard work). Sometimes I have to repeat the acknowledgement as they didn't get it the first time, as you note, after looking closely to see if they got it or not -- it's usually obvious when it has got through (assuming the acknowledgement/recognition is genuine and not trivial).