Microsoft released two Bulletins this month patching 3 critical vulnerabilities. Along with these immediate issues, they released five other Bulletins rated "Important". It appears that the two critical Bulletins address use-after-free vulnerabilities that can all be attacked through Internet Explorer.
For the Windows workstation environments, all versions of Internet Explorer need to be patched asap, including v10 preview running on Windows RT. The patch for Internet Explorer 10 on Windows RT is available at the "Windows Update" site.
In addition to the privately reported vulnerabilities in Internet Explorer code itself, the Remote Desktop Connection v6.1 Client and Remote Desktop Connection v7.0 Client ActiveX components on XP, Vista, and Windows 7 are vulnerable. Microsoft's SRD team expects to see exploits available within 30 days targeting CVE-2013-1296.
Of the "Important" vulnerabilities, interesting to note is a privately reported Elevation of Privilege issue CVE-2013-0078, which is a bug in the Windows Defender anti-malware engine running on Windows 8 and Windows RT. This vulnerability could be used by an insider or determined adversary to gain further access, and not a type of vulnerability usually hit by mass exploitation kits. Within organizations, this is something to quickly address, but generally individuals do not need to urgently address this type of issue.
See Microsoft's Security Bulletin Summary for April 2013 for the full list of this month's Bulletin releases.