Thumbing her nose at this whole winter thing, Opportunity drove 20 meters yesterday, sol 2,240, on the winter solstice. Granted, Opportunity's landing site is much closer to the equator than Spirit's, so she doesn't feel the winters nearly as much as her sister, but she has still been reporting pretty darned low power levels -- 249 watt-hours as of sol 2,239 (May 12). It's still enough to drive on, though! Keep on truckin', Opportunity!
The current strategy (as reported in the latest rover status update) is to drive Opportunity short distances to "solar energy 'lily pads,' places with a modest northerly tilt." The northerly tilt improves the angle with which her solar panels catch the rays from the Sun, which, at the winter solstice, travels much closer to the northern horizon than it does during summer.