Administrators can celebrate
Even with extensive planning, upgrades are never easy – at least not in my experience moving to MOSS 2007 from earlier versions. But stepping up to 2010 will be far less of a hassle. For starters, existing sites can convert with the existing MOSS 2007 user interface, including any customisations. Then, site stewards can preview and switch to the new user interface when they're ready. There's also an upgrade checker that helps you identify custom code that might be replaced with out-of-the-box SharePoint 2010 features.
For day-to-day management, the streamlined Central Administration console provides new tools for throttling activities, such as bulk jobs or asynchronous tasks, to help prevent the server from slowing. Additionally, I liked health reporting, which pointed out where my server configuration could be improved.
This information is available from a much improved web-based administration interface. On the flip side, the new PowerShell command line interface automates common steps. It ships with hundreds of "commandlets" for doing most anything from creating sites to updating user permissions.
Given that I was running beta code, SharePoint Server 2010 was fairly complete and solid. Be mindful that it's 64-bit, so you need Windows Server 2008 and 64-bit Microsoft SQL Server 2005 or 2008. And you'll have a better experience with Office 2010. Otherwise, exercising the beta should give you a head start on planning your migration.