Does having lots of apps open slow down the iphone?

I keep double clicking the home button to completely close down open apps, does this really keep the iphone from slowing down?

If you have a lot of apps open this can slow your iPhone down.

You may also find that open apps access the Internet that can also slow down your data connection, particularly if you are using 3G.

It is recommended that you do close down the apps you don't use that often using the double-click home button method.