…unless you're intending to leave various applications installed because you don't have their installation discs and the buyer is paying for their inclusion.
If the apps installed were obtained legitimately, then the various installation CDs and DVDs would be available to the buyer.
If the original CDs and DVDs were "lost," there is no reason to keep the installed apps on the hard drive.
Any buyer who's worth their beans would demand the original installation CDs and DVDs for installed apps that they are purchasing. If I were the buyer and the seller was only willing to provide me with the installed apps and not the original installation CDs or DVDs, I would demand that the seller lower the price of the computer by the retail price of said software -- or simply walk away.
Every single computer you see on Craigslist or eBay that says, "Computer comes with a fresh copy of Mac OS X Leopard installed and is also pre-installed with Microsoft Office, Adobe Creative Suite and Final Cut Pro" (or something similar) is a computer chock full of pirated (and, hence, illegal) software.
In order for the ownership of a license for commercial software to be transferred to a 3rd party, the 3rd party must be provided with the serial number (and, in many cases, the original installation media). Pre-installed software that's already had the serial number inputted does NOT meet this requirement.
Don't tap-dance close to the "illegal or legal" line... just do the right thing and don't leave installed commercial applications on the hard drive if you do not intend on providing the buyer with the cardboard box and original install CD/DVD that the software originally came with. It's immoral and, in many cases, illegal. Just provide the seller with a fresh, clean, default installation of Mac OS X (just as it would come from Apple if it were purchased brand-new) and let them pirate their own damn software.