Mashable.com has an article on the various websites that have changed their logos to a Valentine’s day theme.

At first, I was inclined to credit (or blame) Google for establishing the precedent of changing your company logo for different occasions and events.
…but I thought about it again I realized this wasn’t true. Does anyone remember Paul Rand’s playful freestyle-mixup of the IBM logo?

Not every designer is Paul Rand, so if you decide to start experimenting with your logo, be careful. You can up with something beautifully unexpected or you can end up with a train wreck.