Apparently it's to do with tooth decay. I started off giving DS little drinks of milk during the day in his sippy/straw cups just before he turned 1 and left him with the night time bottle of milk until he was about 16 or so months, then just switched it over to a cup with a firm spout (like the take n toss cups). He protested at first and the first few times I had to tip it back into a bottle, but I just kept offering in the cup and after a couple of weeks that's all he drank it from.

PS. Love your new avvy Ruf