I read this article published in Realtor Magazine that has some interesting turnoffs for buyers:

Daily Real Estate News | December 4, 2007

Homes Features That Are Big Buyer Turnoffs
Old homes can be quaint, but there's a difference between old and outdated. Unless home owners periodically invest in upgrades, their homes will fall so far below the standards of current buyers that they become obsolete and hard to sell.

What's obsolete? Here's a list of relics, many of them courtesy of Nick Kuhn, an associate with McEnearney Associates in Washington DC.

• A house with only one full bathroom. Even a house with one full bath and a toilet/sink powder room is going to turn buyers off.
• A house without air conditioning.
• Electrical systems protected by a fuse box instead of a circuit breaker.
• Spiral staircases. They're relatively rare, and for good reason - they're often unsafe.
• Basements with only an outside entrance. Home owners expect convenient access to that valuable space.
• Ceilings that look like they've been stuccoed, dropped ceilings with fluorescent lights, and dark beams cutting across the ceiling.
• The split-level floor plan. Want to go from kitchen to family room? Go down half a flight of stairs. From living room to bedroom? Up half a flight. Most folks would rather not.

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In addition to these, I can add a few, based on my own experience:

• Blown ceilings (at least in Charleston every buyer wants smooth ceilings)
• Dark wood paneling
• Shag carpet
• Garden gnomes
• Small windows (that are usually painted shut)