Yes, specific dates have special meanings to organizations such as Al Qaeda, Hezbullah, etc. (Basically anyone as noted by dmckee in the first comment to your question.) The Congressional Research Service has even written a document about this (PDF). The National Counterterrorism Center also has a great deal of information online (although I find that interactive timeline severely lacking).
The United States Air Force considers the significance of dates to terrorists important enough to release something in an unclassified forum.
Terrorists often pick meaningful dates to schedule their attacks. The biggest terrorist anniversaries of the year, however, are April 19 and 20. These dates are extremely significant, especially to domestic terrorists.
Granted, a great deal also spoke about Domestic terrorists. This behaviour is not restricted to Islamic terrorists, but pretty much any radical that has a specific message to convey through violence. It "heightens the impact" as it were.
The Department of State offers this
In the past, terrorist organizations have on occasion planned their attacks to coincide with significant dates on the calendar.
Keep in mind, most assessments and documentation for this sort of intelligence activity is classified either because the sensitivity of the source, or to keep those who would do harm guessing as to exactly what we do know. Documentation will be difficult to find, and unless you restrict your search to specific veins, you may come up with some incredibly irrelevant, not to mention outright wrong, data.
Some additional reports that may aid you in learning more:
Terrorist Motivations and Behaviour (PDF)
Counterterrorism Calendar 2010 (PDF)