A cloud storage service is only as good as the eco-system around it.
This has traditionally been one of the greatest weaknesses of SkyDrive, which worked well for Microsoft's own products (e.g. OneNote 2010 sync) but had little to no 3rd party support.
Contrast this with DropBox. Without a 1st party eco-system to work with, DropBox focused on building a 3rd eco-system through the support of a public API.
With hundreds of apps supporting load/save using DropBox, it's clear they been very successful with this effort
One of the lesser known recent SkyDrive updates is the publication of a supported SkyDrive API which was released at the end of last year.
Since release Microsoft have continued to expand support around the API with SDK's now available for Windows, Windows Phone, iOS and Android. By supporting REST Microsoft has essentially made SkyDrive available to any app on any device with a connection to the Internet.
With the recent SkyDrive client announcement combined with SkyDrive being the de facto standard for cloud storage in Windows 8 metro apps and the public API for all other platforms, I believe SkyDrive will become a major player in the cloud storage market, not just for Microsoft's own products but across the entire range of connected computing devices.
You can read more on the SkyDrive API here.