I still struggle with this. Anything for me that needs creativity or critical thinking (programming and writing mostly) really suffers with the interruptions.
Steven King wrote something that really made me focus on changing this. He essentially said that the difference between an amateur and a professional writer is that the professional write even when not in the mood. That made me think a lot about how I write code etc. and how I can use my free time even when I don't want to when I have to absolutely get something done.