i've been to pie a few times.
and i actually would disagree with what the above person said. you
can in fact buy the pie by the slice.
they have set up a little table / coffee shop area in the back of the store for you to enjoy it. they have a barista and everything, they serve Julius Meinl. They started this about a year ago, so maybe that's also when they started selling pie by the slice, not sure...
and as many times as i've been, i always usually just get coffee. i have had their pie once though, but i don't remember much else other than it was really good