
One needs to remember that Spirit was only supposed to operate for 90 days, so here we are in year six and it is still doing some great science. As you may also recall, in its second year one of Spirit's front wheel stopped working and thereafter the little craft was driving backwards dragging along one of its broken "legs." And even this dead wheel expanded science by creating shallow trenches that told us more about the surface of Mars, including potential evidence of water on the surface. So we are talking about one tough little vehicle that keeps on ticking. By the way, one more wheel died a few months back, so Spirit may not be going anywhere even if it could recover from the sand trap.
So where is it now? Well, NASA wants to continue to use Spirit to conduct "stationary science." However, with the Martian winter starting (the fourth for Spirit), the craft has been put into hibernation with just the right tilt allowing its sand-covered solar panels to recharge the batteries under a weaker winter sun. Spirit will hopefully communicate again when it is ready and its power source is in better shape.
Go here for a good video biography of the little craft that could from NASA. And visit the Spirit's Mission Manager Reports for the ongoing status of the rover.