I am pretty sure it has been proven that Google penalizes for landing pages with popup/popunder windows, because it negatively affects the user's experience. I was just wondering if they do the same for JavaScript-based modal windows? Or if they are even able to detect them??

does that affects the user's experience? if not ,then do it.

I guess it can negatively affect the user's experience?

The only pop-ups that Google permits on a landing page are modal warnings.

What.. Google permits?!!

Sure its ok and google can read anything you put on your website
Including part of flash, CSS, JavaScript and more

If its good for the users go for it.

The only thing google might punish a website for is trying to manipulate search results. From a website point of view that means buying link that aren't meant to drive traffic of clocking text so users can't see it but google can .. Etc..

Hope this helps
Cheers, sagive

Well nowadays a LOT of different things affect search results, including how old a domain is and the amount of time it takes for the page to load. I was just curious whether modal windows had any affect.

i dont think Google penalises you in terms of rankings, but the users can only block the pop up browsers.

yes google penalize this, If we use popup ads and adsense ads the google will also ban you adsense account

All the search engine tries to give user best searching experience. For that i think they don't allow popups ads and other kind of stuff.