Timothy Burke has an elegant defense of Jacques Derrida up on his site. The entire essay is well worth reading, but this section in particular struck me:

Derrida I just sort of shrugged at, and asked, "What’s the big deal?" One of the things that came out of the ensuing conversation was that you sort of had to be there at the right time and place for Derrida’s work to be intellectually transformative, that he was an intervention in the truest sense of the term. I think that’s about right. Just as many of Marx’s critics scarcely recognize the degree to which Marx produced much of the common social and historical frame of reference and vocabulary that the critics themselves use, so too do many of Derrida’s critics fail to recognize how much Derrida and his associated helped to normalize certain propositions about interpretation and communication that we do not specifically attribute any longer to them.

Long-time Hum Dee Dum readers (um… yeah) will surely remember that I had a similar little epiphany a while back—that Derrida gave us muddy and recondite means to pin down what is now, alas, rather obvious. That still seems right. The big doff idea—that any structure and system of signs cannot ever be fully self-enclosed—only becomes truly profound when you see what has been done with it. And even that is an accumulation of inches.

Another way to look at Derrida, I think, is that reading his works makes for a good workout. Mental gymnastics, that sort of thing. Derrida doesn't really teach you to think, but he certainly teaches you to ruminate, and that is certainly valuable. Donald Davidson once hit it on the head when he said that the trouble with philosophy is that it is hard to improve intelligibility while retaining the excitement. Derrida opted for the excitement, but I think that matters too.