There's definitely a place where it gets too extreme. I've caught myself going to check IMs and emails while a page loads in the browser. I pause in my writing at the end of a sentence and I flick my gaze over to check for new mail.

I think the point at which you can switch is when you can honestly expect to give the thing you are switching to your full attention until it is complete. So sure, go answer a few emails during a compile, but only check for the compile to be done in between emails.