See below.
This is exactly right. When you leave your phone charging overnight, it charges to 100% then discharges to 90%, then recharges etc. This is to preserve the health of the battery. All the while, the phone will report that it is fully charged, even though it may be anywhere in the 90-100% limbo.
So, when you disconnect it, it may drop quickly then stabilize its readings to be more accurate.
That all said, please see my battery stats on the last page. In short, way better than the GNex, gets me through a full day easily, but nothing mindblowing. Also, 3G usage uses much more battery than WiFi for some reason. I suspect the phone is constantly looking for the best DC-HSPA connection, but who knows.