Unfortunately, I also have to grade papers (yes, more reading, but with the added plus of giving a grade (yick). Fortunately, the assignment I'm grading seems pretty straightforward, and my comments do not need to be extensive. Still, I imagine grading will take most of the morning--after which I'll be walking in a parade, and then back here by noon to grade again (and hopefully FINISH).
Interestingly, both of these tasks feed one into the other. Certainly, I enjoy reading fiction more than an assignment (with some exceptions, if the fiction is ghastly), but with both I am, in a way, grading. I'm offering grammatical feedback, making notes throughout, explaining my own expectations (whether I am patting on the back for meeting these expectations or telling the writer I want more), and my goals are pretty much the same, as well.
In fact, my main goal with each activity is to make someone else's work better.
And that, my friends, is what has kept me teaching for the last 16 years. And it's why I am usually willing to read other writers' rough drafts, too.