In whidbey, ASP.NET Project Start option has come up with additional option "Use Current Page". When you set this option and run/debug your project, VS.NET will start with the current aspx page that you are working on. If you are working on codebehind file, it will open the corresponding aspx page.
To go to Start option: Select Web Project --> Choose Property Pages option [shortcut Alt-Enter] --> In the property pages, select start option.
Using this feature, you need not select “Set as Start Page" option whenever you want to switch between aspx pages. This option is very useful when you are showing demo where you need to run different aspx pages for each demo. Whenever you change the aspx page for demo, it will start with that aspx page.
Default start option is "Use Current Page", but once you use "Set as Start Page" option in VS.NET. Start option will change to "Specific Page" and it will point to the selected page. In this option, though you move between aspx pages in VS.NET, it will always open with the specified page.
Another tip for "Specific Page" option is, you can specify query string parameter along with the url. This feature is very useful when you want to run/debug an aspx page, which requires querystring parameter for its operation. This feature is available in vs.net 2003 also.