My son is now 16mths and everyday I am reminded that the ability to divide his attention between multiple tasks is one that he does not have - and one that he won't have for many years. That is why as parents we say things like, "look at me when I'm talking to you" and "turn your listening ears on" (my personal favorite because it adds a little humor to the situation). As adults we know that you don't need to be looking at someone to hear what they are saying but when you are talking to a toddler, the first thing you need to do is get their attention.
What this means is that when your toddler seems to be ignoring you, in fact they are likely just busy doing something else. That's the good news and the bad news. I want my son to be able to focus on particular tasks and get really involved in coloring so much that he blocks other things out (hopefully that will translate to his schoolwork someday). The bad news is that I need to call his name countless times to get his attention. The other good side of that is that I was able to sneak into his classroom the other day, grab my keys, and leave again, without him noticing.
So what I've decided is to keep it light, work on turning those listening ears on, laugh when he's so involved in trying to use his spoon to eat his applesauce that he doesn't notice dad came in the room or his cup fell on the ground, be glad he's working on developing the skill of focused attention, and know that in another ten years he'll be able to divide his attention between tasks.