One of my professors once said that he had never gotten around to reading Bertrand Russell's History of Western Philosophy, and probably never would. It was a famous book, but it was also infamous: Russell supposedly impugns those he disagrees with, often resorting to ad hominem attacks, Leibniz being a particular target (allegedly -- I haven't read it either). Anyway, an interesting blog that I've been frequenting of late is I Want a New Left, and he just posted a quote from Russell's History on Islamic Philosophy. It seems fair, insofar as Russell recognizes that the Muslims made genuine contributions in mathematics, but for the most part, their role was limited to 1) writing commentaries on other (Greek or Roman) works, and 2) passing on the ancient texts to western Europe. I would suggest though that genuine contributions can be made via commentary -- I'm thinking in particular of Ibn Rushd (Averroes) and his unusual suggestion in his Long Commentary on De Anima that there must be a nonphysical analogue to matter.
Nevertheless, our desire to recognize the good things about Islam has led to the exaggeration of Muslim accomplishments, crediting them with insights and discoveries made by others. This is unfortunate: when you exaggerate a case, eventually people will find out, and then they'll be less willing to believe similar claims, even if they are genuine.