The wifi and bluetooth transceivers turn off whenever they're not in use. There's no real "standby mode."

As to the 3 day battery life in standby, I really have no way of testing that. Nokia claims 7 days of standby, but, well, my 770 isn't going to be idle for 3 days to test this

Even if that's right, though, that's only about 2 minutes per hour - 1/24 of an hour per hour. As long as you plug your 770 in at night, it really shouldn't matter.

The consensus on #maemo among developers is that 3 days is an unreasonably short length of time for your battery to last in standby; it's also very mean to such a nice toy to leave it alone for so long
At least one person gets 9-10 days of standby out of his.

What does offline mode do that's different then? Or is it purely a switch to disallow the software from bringing up an internet connection?

Yep, it is usefull in a plane etc

So it is an all wireless hardware off switch - what Pocket PC calls Flight Mode?

Excellent