As long as a person does not upgrade various software apps, etc that require a newer version of Windows, you can still run WinXP. Here at the office, all of our CSRs use WinXP and the software is in-house developed. The only app that might at some time require upgrading is IE.
That said, if the time comes that we are forced to upgrade IE, then we will probably have to upgrade Windows. By that time though (probably May 2014) we will be replacing all our workstations and you can be sure that they will be running Win7.
Just ordered 2 new laptops from Dell and got them with Win7 Pro and a "free" Win8 upgrade (if and when we desire to go to Win8)