We've covered a number of problems that people have had with the trash in OS X, and a few months ago I wrote aon how to remove and reset the trash in OS X, which can be used to clear a few common trash misbehaviors. While various problems such as those we've previously covered can happen to the OS X trash, there are some built-in behaviors that may appear as a problem if they are activated when people do not know it.
The primary one is with the "Secure Empty Trash" option, where if enabled it will take a lot longer to delete items since it performs a multiple pass write to the area of the disk where the files resided. Albeit a rare occurrence, system updates and upgrades have resulted in the secure empty trash option being enabled for some users. Additionally, the option may have been turned on and then forgotten about, or been turned on by another user.
If your trash is taking a while to delete, and especially if it takes longer for larger files, then go to the "Advanced" section of the Finder preferences and uncheck the option to "Empty Trash securely" if it is enabled.