How current are satellite maps?

Satellite maps are as current as when they taken and depends on the satellite provider and/or source for the imagery.

The base imagery, for example, in Google Earth and Google Maps is on average 3-5 years old. Weather imagery and overlays in Google Earth on the other hand are updated an hourly basis. Satellite imagery is Google Earth/Maps is incrementally updated usually about every 2-3 weeks in whatever area an update is available -- the entire globe isn't updated all at once.

Likewise, Bing Maps updates its imagery once a month with typically more than 10TB of imagery, but its aerial and Bird's-Eye images for a particular location can sometimes be several years out-of-date.