Starting today, Windows XP computers configured with Automatic Updates will begin to download and (depending on the configuration) install Service Pack 3. There are a few minor new features aiming to  benefit corporations that are still using this OS, other than that, no real improvements that ordinary/home users will benefit or see from it. Microsoft have ceased the distribution of Windows XP on June 30th, the only way users will able to obtain XP on a new system is perhaps have the manufacturers install it (downgrade) as an option, install it themselves, or buy an Ultra Low-Cost PC (ULCPC). . Microsoft will end support for XP in 2014, which still give end users of this aging OS some times before having to upgrade. Hopefully, by then Vista will have become significantly improved or maybe Windows 7 will have come out as another option for users.

As far as what XP SP3 can break, as of current time we know that SP3 does not work well with some web-based VPN such as SSL Explorer, Juniper, etc.