Many large corporate backup vendors have been immersing themselves in the consumer market as well. EMC Corp. is among the leaders with its MozyHome product, which it added to its product line with the acquisition of Berkeley Data Systems in 2007.

In March, security software vendor Symantec Corp. launched a simple backup service called Norton Online Backup, marketing it as a consumer product for managing up to five PCs on a home network through a single dashboard. The block-level, incremental backups are encrypted both in transit and at rest in Symantec's data centers.

Symantec offers 2GB of online storage for free with its Norton 360 security suite; additional allotments of 5GB, 10GB and 25GB a year can be purchased for $29.99, $49.99 and $69.99, respectively.

in 2007. SkyDrive is unique in that it is essentially free. While most services offer some free storage -- 1GB or 2GB -- to whet users' appetites, SkyDrive offers up to 25GB of online storage capacity at no charge; the only caveat is that individual files can't be larger than 50MB. SkyDrive doesn't offer any sophisticated tools, such as incremental backups or encryption. Microsoft makes its money from advertising on the SkyDrive site.

"Think of it as a [flash] drive in the cloud," says Dharmesh Mehta, director of Windows Live product management at Microsoft. Mehta says what will differentiate SkyDrive from other online storage offerings is that it's about to be combined with Microsoft Sync in order to offer not only storage, but also content sharing and collaboration services through the LiveMesh beta.