1. If your username contains a dot (.), then you can also login to your google account by skipping that dot.
E.g: abc.xyz can be accessible by abcxyz. (but account login will be displayed as abc.xyz)
2. If your username doesn't contains any dot (.), you can split your username by placing any number of dots (.) & try to login to your account.
E.g: if my login id is abcxyz then I can use either abc.xyz or abc.x.y.z or abc...xyz etc. (whatever combination you want).
This is because Google has started to ignore periods.
So, you can take advantage by creating several Email Alias of your single Google Account & use them for different purpose.
E.g: abcxyz for your personal use, abc.xyz for friends etc.
I have tried all above test cases & works fine for me. There may be some exceptions E.g: If two different people created two different login as abcxyz & abc.xyz etc. I haven't tried this but I hope this will also work.
This is (may be) just like the Email Alias in outlook.com (previous hotmail.com).
Have Fun !!!!!!!!