Recently I had a little incident. Guys at work were playing with my Android phone lock trying to figure out the right pattern. Unfortunatelly they failed and after 5 attempts the phone asked for my Google login and password. To my surprise when I entered it the phone decided that it was wrong and I couldn't find a way to get into my phone until I found a usefull post here
Putting my Gmail login and password 'null' allowed me to set up a new lock pattern :) hurray!!
Nice security gap ;)