What happens when you login into 1 Gmail account simultaneously from 2 different computers? Can this cause any problems? If so, what are they?

Thanks in advance.

No problem with that.

I think you should be OK though it will be logged, you can access your Gmail log by scrolling down in Gmail. You will see the text "Last account activity: [n] minutes ago on this computer. Details" Clicking on Details opens the activity from other IPs...