Many organizations have some kind of SharePoint deployment, whether it is a full intranet using SharePoint Portal Server 2003 or a collection of disconnected Windows SharePoint Services sites to manage department or project documentation. The idea of upgrading these sites to the newest version of SharePoint can seem a daunting task, especially if you remember/experienced a similar migration path from SharePoint 2001 to your current implementation. Though the effort is not trivial, it is well worth it, for the features and improvements in the new version.
Here are some of the key benefits gained from the previous version, broken down by SharePoint version.
SharePoint Portal Server to Microsoft Office SharePoint Server
Web Content Management - SharePoint now offers WCM capabilities, like browser-based page editing, reusable content, site collection image libraries and content scheduling. SharePoint also has cross-server deployment capabilities, to ensure that deployments are scheduled and controlled.
Business Data Catalog - The Business Data Catalog provides the SharePoint instance to use line of business data (from SQL, Oracle, SAP, Siebel, et cetera) in lists, web parts, and search.
Excel Services - Excel Services allows viewing Excel Spreadsheets on the web (no Excel need be installed on the client). Excel services will also perform scheduled recalculations of the spreadsheet. The web parts available to view the Excel sheet are also very powerful (no more Office Web Components!! Woohoo!), giving organization the ability to quickly create dashboards of their critical business data.
Forms Server - Forms Server allows for the storing, managing and viewing of InfoPath forms via the SharePoint server. InfoPath forms can now be published as web forms, by passing the need for the InfoPath client to be installed.
Search - The search in SharePoint hass been completely redone. The search that comes with MOSS is a fully-capable, customizable enterprise search. For search alone, I believe many organization would consider the upgrade.
Windows SharePoint Services v2 to v3
Workflow - Workflow in SharePoint fully leverages the .NET Framework 3.0. However, there are still two options here. Workflows in SharePoint can be designed in Visual Studio 2005 and deployed as a feature (assembly), but they can also be designed by business (non-technical) users in SharePoint Designer. The SharePoint Designer interface is wizard driven, intuitive and surprisingly powerful.
Event Handlers - Synchronous and Asynchronous Event Handlers (for all list types, not just libraries). See here.
Content Types and Site Columns - Content types and site columns allow companies to define metadata at a higher level than the list or document library. This means that you could define a content type called "project plan" and another called "design specification." Both columns could reuse existing site columns, such as "project type" and "business line" but could also define their own fields, specific to those content types. Then SharePoint sites across the organization could leverage that content type on multiple libraries. Content types also define the document template to be used for that content type, minimizing the deployment of new document templates.
Search - Even the search in WSS has improved. WSS is no longer leveraging SQL Server Full Text search, and instead is using a newly developed indexing engine, which is much more robust.
Solutions and Features - Solutions and features make up a new deployment model for enabling new capabiliteis in SharePoint. Not only does the provide a more succinct mechanism for deploying capabilities, but audit of thos capabililties as well.