Perpetual iPad Tether to iPhone?

[mainstay]

I've seen similar posts but none that asks specifically this question:

When you tether your WiFi only iPad to your iPhone to use it's data plan, how permanent is this connection? Will this survive powering off either device? Will it survive an iOS 5 upgrade?

Does anyone ever leave their tether in place perpetually?

Do you ever have to go in an reset the connection? How often?

I get that there are battery consumption issues + the possibility of paying more for over usage charges than you would for a data plan for the iPad....

are there any other concerns?

Thanks!

--m