Tomorrow is also the day that tools used to block the downloading and installation of XP SP2 will also stop working, and so machines that have automatic updates of XP will be receiving that update.
Meanwhile, there is some speculation that hackers will try to exploit the above events, with e-mails claiming to be from Microsoft but in fact coming from said malicious hackers. Something along the lines of the recent eBay, Paypal and Amazon efforts will no doubt be in evidence, with a bogus link to a Windows Update site. Naturally, anyone taken in by this will then install Trojan code on their machine which opens a back door that allows the PC to be remotely controlled. So, be warned! Verify the authenticity of these sorts of mails before opening and replying to them, especially with sensitive information such as passwords and credit card details.