The Associated Press writes that marketers and Web sites alike are struggling to bring to the Internet ads that resemble television without turning off viewers the way TV ads often do:

"Spending on online video ads represents less than 4 percent of all Internet advertising and just 1 percent of the amount spent on TV, according to eMarketer. But growth is expected - with the research firm forecasting U.S. spending more than tripling to $4.3 billion in 2011 - especially as more viewers embrace full-length TV episodes and other video online."

The challenge, the report said, is finding the right formula—in the creative approach, the format or the frequency with which the ads appear—so visitors notice the pitches without getting so annoyed that they never come back.

We've commented on various stunning revelations in the past about mobile advertising, where prerolls are too long, and viewers are generally less likely to put up with them. There's another trick with mobile advertising, though; on the desktop, users can do other tasks:

"For the most part, I just mute the volume," said Frank Harper, who runs a VA-based security consulting firm, in the report. "Or I just look at something else, look at another headline ... or go to another site while the thing is playing."

Whereas on cell phones, there's nothing you can do but sit through it.