In tandem with this week's consumer launch of Office 2010, Microsoft has also begun rolling out its next-generation version of the Hotmail web-based email service. But if you're waiting for the new version, it's unclear how long you'll wait, as it's a staged rollout, with some users getting the code immediately and others waiting for an unknown period of time.

"If you don’t see the new features today, please hold on just a little while longer," Microsoft Program Manager Mike Schackwitz explained in a blog post. "Everybody will be upgraded this summer."

The tiered rollout happens because Microsoft's Hotmail servers are grouped into clusters. "And we have hundreds of clusters," Schackwitz explains. "We start by upgrading a single cluster, wait to make sure that it's running smoothly and that we didn't miss anything during testing, and then we continue on to the next cluster." These clusters aren't location-based, so customers from around the world will be upgraded simultaneously.

The new Hotmail features a slightly revised UI, but numerous new features, including anti-clutter tools, integration with Office Web Apps (OWA), huge new attachment limits thanks to SkyDrive cloud-based storage integration, and more. Some features, unfortunately, are locale-specific. So, OWA integration will first roll out to Hotmail customers in the United States, Canada, United Kingdom, and Ireland, and then to customers in other countries later in the year, according to Microsoft.

For more information about the new Hotmail, please refer to my multi-part Hotmail review on the SuperSite for Windows.