Assuming that once defrosted, I'd most likely use them for their juice (but not exclusively; I occasionally use the peel for zest, whole slices for cooking with fish/poultry or preparing vegetables in brine).
Is this even possible?
After a quick Google search, I found chowhound topic that deals with this exact matter. They'll grate well and it's handy when (just semi-defrost them) you need some grated zest as you can just pull out a bag from the freezer and sprinlkle them into your recipe. They'll juice but you need to defrost them which I'm told is best done by 'zapping' them in the microwave for 30 seconds. Apparently you get more juice after they've been frozen as it bursts the cell walls releasing more juice.
Hope this helps!