According to Nielsen/NetRatings, around 12 billion searches were completed by the top five search engines in the second quarter of 2005. With Google, Yahoo and MSN raking in big bucks with pay-per-click ad services, smaller and specialized search players launching, marketers' heads are starting to spin.

Search executives and marketers will converge in San Jose this week for the Search Engine Strategies conference. There, they will try to make sense out of a landscape that's shifting quicker than Angelina Jolie's lovelife.

MSN didn't respond to a request for comment about whether it would officially launch its pay-per-click ad platform, which already is up and running in Singapore.

"I think they're getting this quietly up and running," said Danny Sullivan, show director and editor of Search Engine Watch.

MSN has been testing a homegrown pay-per-click advertising platform, designed to integrate with the site's other advertising products. Executives said the service, dubbed MSN adCenter, would let search engine advertisers take advantage of the demographic and individual information MSN has gathered about users to target ads in other ways besides keywords.

The proliferation of pay-per-click advertising services, with Ask Jeeves opening its up to all advertisers on Aug. 15, makes search engine marketing more complicated, said Fredrick Marckini, CEO of search marketing firm iProspect.

"It will be a more complicated game to maximize your ROI over multiple platforms," he said. Many large marketers use automated keyword bidding platforms, and their software will need to be ported to the various search engines' pay-per-click platforms. Smaller advertisers that don't use automated bidding applications may not bother to try out the newcomers.

"If it's not a lot of volume, it's certainly a lot of work raising and lowering bids for what may prove to be a small amount of traffic," Marckini said.

A panel at SES will discuss whether bidding software can replace humans, according to Sullivan. He said panels at the show would hit topics close to marketers' pocketbooks. For example, experts will pore through patents and patent applications filed by the major search engines in an attempt to find clues to help marketers increase their sites' rankings in search results.

With the proliferation of Web-enabled cell phones and portable devices, mobile search has become an important way for companies to connect with consumers. Yahoo launched an SMS search product in July, while extending Yahoo Search on Mobile to WAP (define) phones. That same month, AOL untethered its own search services with the release of AOL Search service, Pinpoint Shopping Search and AOL Yellow Pages for mobile phones and devices.

While tools are still developing, audio and video search have become a hotly contested area, with loads of new content coming online and a variety of strategies for indexing.

TVEyes, which has long provided a professional, subscription-based search service for news content, began offering PodScope, a free podcast search service, in April. Blinkx began integrating content from video blogs and podcasts to its Blinkx.TV service in June.

On August 4, Yahoo added Yahoo Audio Search. The specialty search service lets users preview an individual song or artist from 16 different services, including the iTunes Music Store, Napster, Rhapsody and Yahoo's own Music Unlimited.

Nielsen/NetRatings said image search was the main driver of search growth for the top five search engines last quarter. MSN Image Search grew fastest at 90 percent, with AOL Image Search growing 74 percent and Yahoo Image Search growing 55 percent. Google, with the oldest and most established image search, grew just 12 percent, but it completed more than three times as many image searches as Yahoo, the next highest in volume of searches.

TVEyes CEO David Ives said he's talking to companies such as news organizations that have large video archives about enabling keyword search through the video files.

"I think the value, particularly in the news content business, is to allow users to type in search terms and watch video no matter when it was. The service could be ad-supported just by the sheer traffic volume you'd be able to generate," he said.

"Now that consumers have broadband and are downloading audio and streaming video, we will be seeing more use of multimedia search," said Yankee Group analyst Su Li Walker. There also will be more partnerships between content owners and search services, she said.

"The giants will do interesting things, because they have the power to make things happen," Walker said. "Because of the Yahoo and AOL names, they're able to form those partnerships, while the small startup has challenges."

Audio and video is just one category of vertical search, a very hot topic. Several blog and RSS search engines make it easier for those in the know to identify feeds, while Google has been adding some blog content to its regular search service.

"I've been trying to hammer home to search marketers that vertical search is inserting itself very significantly into regular results," Sullivan said. "When you do that search on Google, you might be getting news and local results that push regular results below the fold."

Yankee Group's Walker said that specialized blog search services still are used mostly by early adopters. "The mass market will be heavily reliant on the top five search engines," she said.

Marckini of iProspect said that search marketing has gotten respect at the highest levels. "In the early 1990s, it used to be the assistant coordinator of online marketing who called to investigate a few agencies," he said. "In 1998 and 1999, it was the manager of online marketing. In 2000 and 2001, it was the director of online marketing and e-commerce; in 2002 and [2003], the vice president of e-commerce. Now, we're getting participation at the highest levels of the organization."

This article originally appeared on InternetNews.com.