if you want to prevent running multiple instance
of the same c# application then check the
following lines.It's sometime necessary to prevent
running multiple instances of the same application.

command objects use parameters for passing values
to sql statements for type cheking,validation,guarding
against SQL injection attacks,etc.so its a good practice
to use command parameters to sql statements.

It's required that you configure your joomla SMTP settings so that joomla is able to send
email when user registered or different mailing functions works for other components and modules
like k2, CB....
In this post i show how to configure joomla 2.5/3 smtp settings properly.

Gravatar.com is used to store one's avatar image according to email.
then if you comment in any application using your that email address
where gravatar image has been programmed then your avatar image will
be displayed in the application.

using asp.net membership Probvider you can easily
make a user login using username and password and redirect to
default or any page by the following way -

Asp.net caching helps you to create high performance applications.
you can cache objects like DataSets,or your created objects.you can
also do page level caching if you used user controls in the page
if your aspx page includes lots of work.