For one project that I'm working on, they have a very strict firewall setup which restricts SSH access to only internal machines and those temporary machines outside the network that need access ( like if you're working from home ). So as my IP address changes at home, I need to notify the service that my IP address has changed from A to B. The service prefers if I can give them both the old address and the new address because they'll take out the old address from the firewall rules and add access for the new IP address ( yes, they are that anal ). I was keeping this list on a pad by my desk but today I found myself downstairs, away from that pad, so I couldn't find my previous IP address, just the new one.
Fearing that I would have to walk ALL the way upstairs to get that pad, I thought for a few seconds and remembered the "Details" link in the footer of my gmail page. Clicking "Details" in the footer of gmail will show you the last 10 instances of logins/refreshes to your gmail page. Sure enough, I was able to find the number 7 entry was from last night and showed my previous IP address. I copied it into my firewall request and got back to my work.