ClickOnce is a new deployment technology in Visual Studio .NET “Whidbey” to build onto the existing support for deploying smart client apps with the .NET Framework and Visual Studio .NET. ClickOnce promises to help solve a lot of common deployment issues that developers are faced with today, such as security restrictrions, desktop interaction, runtime requirements, and other deployment tasks.

Despite all the marketing hype about xcopy deployment for your smart client apps, you're in for a lot of work if you have to deploy your Winform apps today. Specifically, with .NET 1.x, you have the following tasks to solve on your own:

• Deploying the .NET runtime to the client desktop. Should you build an installer to install both your application and the .NET runtime at the same time? Or, should you do an SMS or Group Policy push to get the .NET bits installed? What about service packs and MDAC components? See MSDN for further guidance.
• Security context and trust. Apps downloaded by default from the local intranet or internet have a limited set of permissions. With most .NET apps today, this is a problem because a lot of common functionality from the OS is simply not available to .NET by anything or than interop or 3rd party component suites. Thus, unless you truly want a very simple application, you're going to have to add trust to your application through Code Access Security (CAS), which requires administrative interaction.
• Offline support. You will have to consider what level of offline support you want to offer your users. It could be as simple as persisting some datasets to disk ala. TaskVision or Northwind Unplugged, or you might have more data intensive requirements that would require a local data store such as MSDE.
• Automatic updates and versioning. With .NET comes to the ability to easily auto-update your apps and there are several options to choose from, such as No-Touch Deployment, the Microsoft Updater Application Block, or simply calling Assembly.LoadFrom(...).

ClickOnce technology is supposed to help us with a lot of these concerns. VS.NET Whidbey will offer enhanced support for bundling your ClickOnce applications so that you can also deploy other modules, such as the .NET Framework and MDAC, rather than trying to bolt them on with a Windows Installer package. One of the other neat features of ClickOnce is the Windows Shell Integration support, which allows you to add shortcuts to the Start Menu and do other customizations to the user desktop.

If you'd like to see a step-by-step walkthrough of deploying a ClickOnce application, Brian Noyes outlines the steps required to deploy a simple app using ClickOnce with the Whidbey demo.