In case you missed it - there is now less than 18 months of extended support for the venerable Windows XP platform left.  The key takeway from that statement is that there will be no security updates for XP released after April 8th 2014.

In the Enterprise space it's not uncommon to have a migration phase of 12-18 months - which means you should already have a definite completion date set for any planned XP migration/upgrade/refresh projects.

Further details:
http://windows.microsoft.com/en-us/windows/help/end-support