Dear all,
first of all thank you very much for your precious help 
Today I have received my little toy.
I have started playing with it ...migrate the OS on a new SD, configure the newtwork and everything was working perfectly.
Then I deceided to do the openwrt upgrade (1.5.3) and it has worked...beside the USB LED always ON.
The wifi works perfectly, I can use SSH smoothly ...the only problem is the annoyng USB LED as reported in the attachment
If you could help,
I will be greatfull
Thanks in advance
Lorenzo

pedrobrio:
...the only problem is the annoyng USB LED as reported in the attachment
This is normal. The white LED is labeled USB, but in reality it is simply an indicator that the Linux portion has fully booted up. Your Yun is working correctly.
pedrobrio:
::::SNIP:::
The wifi works perfectly, I can use SSH smoothly ...the only problem is the annoyng USB LED as reported in the attachment
::::SNIP::::
@pedrobrio,
There are a number of LEDs on the Arduino Yun. Some can be turned off, some not; some can be controlled.
Here is some documentation on those LEDs.
http://codesnippets.altervista.org/documentation/yun/leds/leds.html
More details on the Yun here:
http://codesnippets.altervista.org/documentation/yun/index.html
Best of Luck
Jesse