Who lives around the corner?

When university lecturer David Wyman began searching for a house near Baltimore, he knew he wanted one thing: a home on a golf course outside the flight path of wayward balls.

"If you're a golfer, you know you never want to buy a house 200 yards down on the right side of the fairway," Mr. Wyman says. "You know you're in a ball alley."

Armed with the URLs of real-estate websites, he explored homes for sale. And with the help of satellite photos on the Internet, he perused golf courses from above. It didn't take long for him to find the perfect home.

The Internet has long been a handy tool for house hunters. But it has become even more useful over the past couple years as sites have popped up to allow people to explore neighborhoods from the sky, read environmental reports, and even learn where not to live. "I love that you can do stuff like this," says Wyman, who has since moved to South Carolina, again with the Internet's help. "It's tremendous."

Millions of Americans share his enthusiasm. Zillow.com, a real-estate site that's barely two years old, says users have looked up individual price estimates for 37 million homes in the United States. An estimated 4.5 million visitors dropped by another leading site, Realtor.com, in December, according to comScore Media Metrix. And several hundred thousand people have posted comments to Rotten Neighbor (www.rottenneighbor.com), a site devoted to exposing ... well, the site's name says it all.

Brant Walker, a 20-something entrepreneur from San Diego, created the site after he moved into a new apartment and noticed an awful smell coming from next door. He complained to the landlord and the neighbors, but had no success getting anyone to take action.

"I thought, 'What if there was a website or service out there that allowed potential home buyers and renters to find out about bad neighbors before they moved? Maybe we could have avoided living in this apartment,' " he says.

And so Rotten Neighbor was born, allowing residents across the world to post anonymous comments about barking dogs, loud parties, and scurrilous teenagers.

"Always cursing at her cats ... and fights with her husband," complains a New York City post. "This dude ... needs to fix this home it is horrible," says a punctuation-challenged resident in Cleveland.

Big cities such as Los Angeles, New York City, San Diego, Chicago, and Houston draw the most posts, Mr. Walker says. Negative posts are by far the most numerous, although it's possible to say nice things about neighbors and also request deletion of especially nasty posts.

Walker, who's shopping for a new place to live, plans to consult his site and others for guidance. "I can't imagine not looking online while looking for a home or an apartment," he says. "That's always going to be my first step."

Real-estate gurus caution that there are plenty of caveats about shopping for a house online. Satellite views of neighborhoods can be outdated. And information about home prices is sometimes misleading.

Zillow.com, for instance, says that its "zestimates" of home values, derived from a proprietary formula, are usually close to the ultimate sale prices. But Wyman and his wife, Elaine Worzala, discovered that the computers behind Zillow don't always know what's going on at street level.

The site listed their former home near San Diego as worth $500,000 more than it actually was, says Ms. Worzala. The site apparently calculated the price by evaluating home prices by ZIP Code. But it didn't realize that the homes east of a freeway, like hers, were farther from the beach and therefore less expensive.

Real-estate websites have done "a world of good" by allowing buyers to avoid being dependent upon real-estate brokers to show them available properties, Worzala says, "but you have to double-check things."

The same advice goes for sites that offer photo or video tours of for-sale properties. Nothing beats an in-person visit, says Sarah Hromack, editor of Curbed SF, a San Francisco real-estate blog.

"In an online real-estate listing, professional photography can skew bad architecture and mask a multitude of contractor's sins, as can sparkling descriptions and even fudged square-footage figures," she says. "You've got to look at the house in real life, ask questions, and check out the neighborhood on foot."

Realtors can be helpful, too. "Some of them are real experts on the specific neighborhoods and have a lot of random knowledge that wouldn't come across in Zillow," says Rich Toscano, a real-estate columnist in San Diego.

In other words, house hunting – alas – can't entirely be accomplished while sitting on your couch with a laptop. To do it right, you'll still have to make real visits and talk to real people.