I have written a number of times throughout the years here on this blog and in other articles about how important it is to backup your critical data.
Recently, especially in the last two years, with services offering to do this back-up for you automatically in the cloud as part of value-added services has caused many people to not take action on backing up their own data.
Two incidents have really highlighted the need to do your own data backups in addition to saving your data with some of these automatic services. One is the T-Mobile Sidekick, in which people using the device have lost their personal and other critical information, and the other, has to do with a flaw in Apples Snow Leopard OS, known as the Snow Leopard Bug, in which all saved data gets wiped out.
I have included links in the reference section that will tell you how to specifically avoid these particular pit-falls. However, I stress just one thing...
BACKUP Your DATA