There are a lot of reasons to upgrade from SharePoint 2007 to SharePoint 2010. There are also a lot of reasons to upgrade to the new 2010 look and feel. But it’s not a requirement, and, in fact, can potentially add a lot of work to your migration effort.

In order to justify this extra work to a client, I’ve compiled a list of advantages the new 2010 UI gives one over sticking with the old SP2007 look and feel. Most items come from posts listed in my SharePoint 2007 to SharePoint 2010 Upgrade Resources post.

Here’s the list:

• explicit use of strict DOCTYPE provides better standards compliance, more consistent look and feel across SharePoint pages, and better consistency and support from a cross-browser perspective
• access to the new ribbon UI
• better general ease of use through the ribbon, menus, dialogs
• aligns better with current Office look and feel
• better use of modern CSS/HTML tags (uses div tag for layout vs. tables, for ex.) resulting in faster rendering and more maintainable pages/sites
• if not using the new 2010 interface, users will not have access to the ribbon, in-place editing of Wiki pages, interactive calendars, cannot define list relationships
• new sites created after the 2007->2010 upgrade automatically default to the new 2010 interface (requiring manual change to the old look and feel each time)
• fully XHTML compliant WCAG 2.0 AA level accessibility (for the impaired)
• AJAX/Web 2.0 enhancements greatly reduce page refreshes
• in-place page editing

I don’t doubt there are many more reasons, so consider this list preliminary or something to build on.