Sorry, folks, Cyber Monday is a myth. An invention of the retail industry to make you think that everyone else is shopping online. According to Snopes.com, it's not usually even in the top ten among busiest online sales days - it comes in 12th.
The term was coined by a retailing organization looking for a counterpart to Black Friday, and it has become a busy day for online retailers (I just realized that I ordered something online today! It was work related, though) and there may even be some records set for the year to date - but stay tuned. As far as the biggest sales days online, the Monday and Tuesday in the two weeks before Christmas have been bigger.
Just like Black Friday has never really been the biggest shopping day of the year (the Saturday before Christmas is), Cyber Monday has never been the biggest online sales day. So don't be discouraged if your Cyber Monday isn't what you hoped. Get ready for the 8th and the 15th.