Boot Camp Software Update 3.3 supplies revised Windows support for Macs running Boot Camp 3.x, included as part of Mac OS X 10.6 Snow Leopard. Apple only notes that update supplies "critical bug fixes and hardware support."
This update is targeted at users running Windows 7 in either the 32 or 64-bit version via Boot Camp 3.2 on Snow Leopard.
Macs running 10.7 Lion do not need the update, as that version (Boot Camp 4) can upgrade itself. Users running Boot Camp 3.2 can download the new package through Software Update or from Apple's download page.
Apple released a "Boot Camp 3.2 update for Windows 64-bit" yesterday, which it states that it added "support for the ATI-Radeon HD 5870 graphics card, Apple USB Ethernet Adapter, MacBook Air SuperDrive, and addresses critical bug fixes."
That update addressed users of Windows XP, Vista or Windows 7 running BootCamp 3.1 on Snow Leopard.
iMac Graphics firmware updates
A second update released today "fixes a graphics issue that may cause an iMac to hang under certain conditions."
Apple doesn't specify which iMac models the firmware update targets, but the package will only install on applicable models and requires Mac OS X Lion. iMacs that need the update can download it through Software Update or from Apple's download page.