I use the Eheim feeder to feed 3X per day whether I'm on vacation or not. With NLS 1mm it works great. Daiichi Veggie FX cakes up due to the humidy and any flake food is a problem. Eheim also has a new feeder that supposedly works with flake.
redrum: When I've been gone, I have left pre-measured food rations ("snack size" ziplock type bags) with the date written on it that particular bag should be fed to the aquarium inhabitants, and a key to the family members who live nearby. They attended every third day to feed. It was my opinion that my fish could eat once every 72 hours for the 10 days I was gone, and be none the worse for it. In fact, when I arrived home from that last vacation (sadly, 2005) I had about 15 new fry in my Species Black Kiriza setup. I think they enjoyed the privacy.