Why does everyone feature a world clock in their information dashboards? Yes, it's a handy feature to have, and yes, it's easy to build, but very few people actually use them.
One of my favorite clock related features is in KMail where it says "Senders current time", which is often helpful as well.
After a while you memorize the time zone differences. But to be sure and take daylight savings in account world clocks are not bad.