For a slice on the go, Libretto's is pretty much aces, IMO. I'm usually hitting up this particular pizza palace late night when I've been watching the fist pumping at Alive After Five for 20 minutes too long. So, yeah, I just want a feed the hungry monster and get on my way home.
Libretto's is pretty basic inside: a front room with a handful of hightops and a back room with standard tables and TV's (I have never been back here). Every time I've been in here (granted it's been after 9 pm each time), I've found tons 'o intoxicated peeps and some folks who were working way too late at the bank of choice. The food is decent and pretty basic - it's a good slice of pizza on the run.
I usually order a slice of cheese or their tomato and mozzarella. They warm your order in the oven, you pay and you're on your way. The service isn't much to speak of - they're friendly and efficient, so that works for me. When I'm hungry and looking to grab some 'za in a hurry, Libretto's is a solid choice.