The marriage license clerk in Las Vegas reports a jump in activity because people want to have 10-11-12 as their anniversary date.

Certainly 07-07-07 was huge back in 2007.

Based upon Chinese culture, the number 7 symbolizes "togetherness". It is a lucky number for relationships. It is also recognized as the luckiest number in the West, and is one of the rare numbers that is important in both Chinese and many Western cultures. It is a lucky number in parts of the Chinese culture, because it sounds alike to the Chinese character meaning arise.

Seven can also be an unlucky number because it is considered spiritist or ghostly. The seventh month of the Chinese calendar is also called the "Ghost Month". During the month, the gates of hell are said to be open so ghosts and spirits are permitted to visit the living realm. However, the Chinese lunar calendar also has the 7th day of the month as Chinese Valentine's Day, so the number 7 is not generally associated with bad luck. In most of the regions in China number 7 remains neutral or associated with luck.

The other unlucky numbers are 4, 5, 6, and 49 (because it is double seven - squared).

Four is an unlucky number because its Chinese pronunciation sounds the same as their word for 'death.' Many of the casino hotel towers don't have floors numbered with fours.
Those missing include 14, 24, 34, 54, 64, all floors between 40 and 49, and the floor number which follows 68 is 88.

On a cheerier note, eight is a very lucky number.

The word for "eight sounds similar to the word which means "prosper" or "wealth". In regional dialects the words for "eight" and "fortune" are also similar, e.g. Cantonese "baat3" and "faat3".

There is also a visual resemblance between two digits, "88", and the character for "double joy", a popular decorative design composed of two stylized characters meaning "joy" or "happiness".

The number 8 is viewed as such an auspicious number that even being assigned a number with several eights is considered very lucky. Many of the airlines flying to China assign flight numbers with 8s in them:

The Air Canada route from Shanghai to Toronto is Flight AC88, the KLM route from Hong Kong to Amsterdam is Flight KL888, the United Airlines route from Beijing to San Francisco is Flight UA888 and so on.

I think it's interesting that what makes a number good or bad for the Chinese has to do with what it sounds like in their language or what the symbols look like. Do we do that in our culture? I'm not sure, let me know if you think of any examples.