SharePoint 2010 introduces a great new way to use InfoPath: InfoPath List Forms. This feature allows you to use InfoPath forms as your editor for list items. Now you get the best of both worlds: a lightweight way to store documents with custom schema and a great way to design custom forms for entering and displaying them. All this, by the way, closely mirrors how things were structured in Notes.
InfoPath List Forms rely on InfoPath Form Services, which means that everything runs in the browser. Happily, there have been a number of dramatic improvements in InfoPath Form Services, and the Web experience really is at near-parity with the rich client experience. And there are plenty of other InfoPath improvements that will reduce the cost of migrating Notes applications, including additional controls, more seamless workflow integration, and automatic offline support.