There was an article this morning in the Arizona Daily Republic of an interview with Dr. Phil Christiansen of ASU about the dust accumulation on the Mars Rovers. Seems that the dust is starting to degrade the power input on the cells. If I remember right, a month or so ago, the engineers were amazed at how little the dust degregation had been. Here's a theory for you on what has changed. The rovers, in their early missions were doing lots of moving - back, forth, up and down. Spirit was doing lots of bouncing over rocks over it's long traverse across Gusev. Recently those rovers have been staying relatively still, only inching around doing primarily grinding and sensing duties in very small areas. I think that they need to be bounced around again to knock off some of the dust, that the long term effect, although the localized science might suffer a bit, will be to greatly extend their lives by keeping them in more motion. Of course they'll have to be kept more still during the upcoming winter.

Sounds like in the next week or so Spirit, which is currently engaged in wheel maintenance activities, will begin its trek up the rocky hill it's at the base of. Hopefully a lot of dust will be vibrated off those panels again as I suspect happened early in the mission. Now Opportunity, once it gets out of Endurance, is in a relatively flat area devoid of rocks and bumps. I think though that it's a more dust free area and just a small increase in movement will help it greatly.

Something else interesting in the last video update from JPL. Guess Spirit's engineers, in trying to fix the problematic wheel, have been doing a bit of reverse driving, dragging the wheel a bit on the ground in an attempt to free it up a bit. You can see the marks from those efforts in the raw navcam images from SOL 188.