Q: stuck on slide to upgrade

Hold down the power and home button for longer than the normal ten 10 seconds (the screen will go black like it's just gone to sleep).

After that it will restart and you will have the same message "slide to upgrade" however this time it should work!

It doesn't work. I encountered the same problem after upgrading my iPad2 iOS today: "slide to upgrade" is unresponsive.

I did a reboot holding power and Home buttons until the device turned off. Then turned it back on and did the following:

Enter password, Apple screen loads...

Get to Hello screen, swipe the 'slide to set up' slider

Enter password again

Get to Update Completed page, click Continue

And boom: Return to the 'slide to upgrade' slider... It's unresponsive

Apple won't chat or accept a call unless we pay $29. Umm......

Here's the fix from Apple:

If the Slide to Upgrade screen won't go away after you update to iOS 9 - Apple Support

Thank you @anypats, unfortunately I'm still out of luck. That solution seems to assume the user has connected their iPad to iTunes. I never have, it's just a standalone device.

In this case, when I connect the iPad to the MacBook and launch iTunes, there's an alert "To allow access, please respond on your iPad..."

Go through the steps above: 

-Swipe 'slide to setup'

-Enter password

-Watch update complete installation

-Get to 'Hello' screen

-Enter password again

-Get to 'Update Completed' page

At this point, there's an iTunes popup "Trust This Computer?" The only option that allows you to continue is "Trust" -- select that

Press Continue on the 'Update Completed' page

Result: The "slide to upgrade" swipe on iPad 2 is unresponsive, and the "To allow access, please respond on your iPad..." popup remains up on the MacBook.

Hard to believe Apple did not anticipate this test case!! So, what, I have a paperweight now?

No mine still refuses to move on

Updating to iOS 9.0.1 fixes the issue..

If your iOS 9 device is stuck on Slide to Upgrade - Apple Support

I found that you have to continue to hold down the Home and Power buttons until the iTunes logo appears.  So here are the steps:

1.  With iTunes up, and your iPhone or iPad connected to your computer, hold the power and Home buttons down simultaneously.  You will see the screen go black, then start to reboot, with the Apple logo displayed.  KEEP HOLDING DOWN THE TWO BUTTONS!  If you don't, it will just go back to the same problem.

2.  After the Apple logo, an iTunes logo will appear (in an image along with a USB connecter showing being plugged into it).  NOW YOU CAN LET GO OF THE BUTTONS!

3.  From here you should be good to go.  My mistake, the first several times I tried, was that I let go of the buttons as soon as I saw the Apple logo.