According to The Record, a favorable ruling for Rescuecom Corp. in April in a long-running case against Google Inc. has fueled more suits, including would-be class actions, against the search giant for selling trademarked keywords that trigger ads alongside its search results.

But in the last two weeks, two AdWords lawsuits -- from Daniel Jurinand Ascentive LLC -- have folded. It highlights the difficulties of the suits, experts say: It's a hard case to make and it's expensive to litigate against Google.

"We're starting to see some of these lawsuits crack," said Eric Goldman, a Santa Clara University School of Law professor who follows the AdWords litigation closely on his Technology & Marketing blog. "My current hypothesis is that they never made sense in the first place -- the plaintiffs got all excited to go take down Google, but suing Google is a loser's bet because Google's going to fight to the death."

In these suits, advertisers accuse Google of selling trademarked keywords to anyone, including competitors. They claim that constitutes infringement because Google users could be confused by links to competitors' ads that appear alongside Google search results for the company's trademarked name.