Hi.
I have updated my raspberry pi B+ to latest kernel 4.0.7-2 and latest raspberry-firmware-* and upon rebooting, I got nothing. Couldn't ssh to ethernet port.
Long story short, I finaly plug it in my TV to be able to see a boot, and found out that as soon as an usb device is plugged in, the kernel panic.
So I removed the SD card and plugged it in my laptop and proceded to downgrade by installing manually the kernel 4.0.7-1 and all raspberry-firmware-*-20150630* packages. And I got no problem anymore.
At first, I thought of an hardware problem because I let it under the sun for one hour. Even though I let it cool 5 minutes in the freezer, I got another panic, the same as before.
Here is the panic
http://i.imgur.com/aLP2IZN.jpg