This looks interesting: a blog about faith, depression, and mental illness. A recent post about pastors dealing with depression caught my eye in particular—I have no doubt that it's a common phenomenon, but I don't know if I've seen anybody specifically address the challenge of preaching while fighting depression or another mental illness:

...depression is the ultimate incurvatus se. You are turned inward, and emotions that are focused outward (like anger or love) are barely on the horizon. Everything is turned inward. So while the good preachers go through themselves in terms of understanding the human condition to preach the Gospel, the depressed person can’t go through themselves. They get stuck. They are in the black hole of their own doubts and fears, and rather than expressing them (theologically in confession, pastorally in preaching, and psychologically in counseling), they simply stew in their own juices so that nothing can come out.

I might also add that in dealing with depression, it is also incredibly hard to take anything in. Reading, meditating, discussing the texts of Holy Writ are almost impossible. So if the depressed pastor... is forced to continue preaching, in pretty short order he will be running on nothing, stuck saying words he doesn’t mean, recycling sermons or copying others' words.

Yikes—that's something that can affect the health of the entire church body. There's another good reason to check in with your pastor and worship leaders periodically to encourage them and make sure they're doing OK.