Pretty much. A li-ion battery will not just stay at 100%. It goes to 100, but then auto discharges down to say 98% or so, then back up. They also only have a limited number of charges in their lifetime. Keeping it plugged in causes a "vampire" effect in which those tiny 100%-98% over and over again take away to the overall lifetime.
I take my phone off the charger the moment it hits 100%. And luckily with my ativ s, its big enough so I don't need to auto charge it at night. I can charge it at like 9am, then noon the next day, etc.
As for calibrating it, my understanding is they don't have "memories" like older batteries, so you don't ever need to condition it. But just like someone above said, don't ever let it die out, its harmful to it, although I can't recall why.
-edit-
Here's a link with some great info.
http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries