In these days one of the (many) tasks where I'm involved is to port a .NET
Windows Form application written with the 1.1 Framework to the new .NET 2.0 and
this post wants to put in evidence some little new features inside Visual
Studio 2005 that permits you to save time and less coding. 
One of the first things that I often found on .NET applications is to check
at startup if the application is already opened and, if so, not open a new
instance but activate the first.
Normally, the code to check this could be something like this (there are
maybe other methods, but this is the simplest):
If
Process.GetProcessesByName(Process.GetCurrentProcess.ProcessName).Length > 1
Then
'I have an
instance already open
End If
Visual Studio 2005 permits you to achieve the feature to
have a Single Instance application without writing any
lines of code. You've only to right click on your solution, choose
Properties and then you'll find these new interesting checkboxes:
Why not all people know these little but really useful features? Print
it on your mind... 
There's only another thing to remember: if you want that VS2005 permits you
to use these new automatic features, you have to check the Enable
Application Framework checkbox (if it's unchecked, you have to code them
manually).
Update: When writing this post I wasn't so precise. These automatic features are available only for Visual Basic .NET projects. If you open a Windows Form C# Project you can't see the checkboxes where to enable these properties. In C# for the moment you've to code all manually (always with the old manner).
Sorry for this new precisation, I use C# but the main part of my projects are VB.NET projects, so I forgot to signal this lack in C#.