Technically, yes, from what I understand, the Nokia Internet Tablets always pull energy from the battery for their operation--even while connected to a charger. So...

That's what I've read, though I haven't tested it. I'd test it for you now, but my N800 and I are temporarily geographically separated from both A/C and automotive chargers.

In any case--barring battery or charger problems--a tablet will, of course, charge its battery when connected to a charger. So, the power an operating tablet draws from the battery will continually be refreshed by power from the charger.

Does the water on a spillway come from the reservoir or the streams feeding the reservoir? And if inflow and outflow are equal, does it matter?

If inflow and outflow aren't equal...

Depending upon the charger used, and the work an operating tablet performs, it's possible to draw power from the battery faster than it is refreshed by the charger. For instance, setting the display to full brightness + "stay on while charging", playing streaming audio or video at full volume, and inserting and removing high capacity flash cards filled with media with media all on a tablet charging via a USB adapter connected to an older notebook computer would lead to "Low battery" warnings in no time.

Is that a problem? Well, yes, it is for you if that's how you intend to use your tablet. They're not designed for that; it's close to worse case scenario for them.

However, under more normal usage, the design works fine. Average web browsing, email checking, and even media playback won't deplete the battery faster than a good charger manage.

That's not to say the battery will stay at 100%. It'll be down a bit at the end of the activity, but not so much that the charger can't top the battery back off quickly.

Also, note I wrote "good charger" above. The A/C adapter that comes with a tablet supplies a fair amount of power. USB adapters generally supply less, and car adapters may be as good as the A/C adapter...or not.

As a bit of a side note in closing, the last version of Canola2 I played with (beta 8?) had (or triggered) a bug that caused tablets connected to chargers to animate the charging indicator in the status bar happily ever after. It wouldn't stop when the battery was full; it would only stop when the charger was disconnected.

EDIT: The mighty Johnx is both faster and more concise.