The UTC ClockNote: If you don't see the UTC Clock on the main page, you don't have Java script active. If you want to see the clock, and some other things on these web pages, you will need to enable Java scripts.
So, why is there a UTC clock on the main page? It's because ALL hams should be aware of UTC time. If you weren't logging contacts before you had HF privileges you should definitely be doing so now - particularly if you are using HF. This doesn't mean you shouldn't be logging VHF and UHF too but most hams just don't log the usual simplex or repeater contact on VHF or UHF.
If you want a QSL card for any of your HF (or other) contacts, you will need to have logged the contact. The ONLY correct time to use is UTC time. This is the only acceptable time on a QSL card for contacts anywhere in the world. Many stations will not respond to a QSL request with the wrong time and if you send a card with local time it will be wrong.
The clock on the main page is based on your computer's clock. If it's wrong, the clock shown will be wrong. If you didn't properly set up your computer's time zone it will also be wrong (usually by 3 hours).
Some other interesting clocks:
The Official U.S. Time - True time from the National Institute of Standards and Technology
The World Clock - Time Zones - Times from around the world
The Naked Alarm Clock - No, it's not what you're thinking. It's just a web based alarm clock
Industrious Clock - probably the most interesting i've ever seen
And of course you can always search Google with "web clock" for all kinds of other clocks.