Using smart cards with Windows 7 requires some extra steps not needed with previous versions of Windows. For example, when you initially logon and then insert your smartcard you still have to press CTRL+ALT+DEL in order to be prompted to enter your smartcard PIN. But if you've got CTRL+ALT+DEL disabled on the machine and log on and insert your smartcard, you'll instead be immediately prompted for your PIN.
On the other hand, if you're already logged on to the machine and the screen saver is running, you have to press CTRL+ALT+DEL to get prompted to enter your PIN. In other words, in this situation you don't need to remove and reinsert your smartcard in order to see the PIN prompt. But if you're already logged on to the machine and it goes into screen saver and CTRL+ALT+DEL is disabled on the machine, then to get prompted to enter your PIN you don't have to remove/reinsert your smartcard, you just have to either move your mouse a bit or press a key on your keyboard.
Mitch Tulloch is a Microsoft Most Valuable Professional (MVP) and widely recognized expert on Windows administration, deployment and virtualization. For more tips by Mitch you can follow him on Twitter or friend him on Facebook.