After her Q&A session at the Search Engine Strategies conference today, I've sat down at a media roundtable with Marissa Mayer (pictured). Among the topics the Google's vice-president of search products & user experience covered were YouTube's evolution, the uptake of the company's mobile services this Summer and "eye tracking".

So let's start with YouTube's recent decision to let users monetise their videos:

"We bought YouTube a little less than a year ago. And from our perspective, generally if you look at our track record we add monetisation anywhere from a year to 2.5 years later. So this is actually reasonably fast. Web search itself ran for 18 months without monetisation. Image search has ran many years without monetisation (it now has ads on the top/bottom of the results page). So, for the same reasons we were not hasty to add monetisation to Web search, we wanted to make sure that we understood what users like and don't like about YouTube. And how to use ads in a way that is respectful of the users' experience."

Google Video is dead, Vive GooTube!

"I overall philosophy will be that we would really like to offer users to upload more content. So I would really hope that in the future YouTube is able to provide for a longer video [currently limited to 10 minutes/100MB]. We certainly have the serving architecture as part of Google Video".

And what about Internet TV (IPTV)?

"It's hard to say what's going to happen in the long term but for certain, right now, our focus is that YouTube is about hosting videos. I think of YouTube as a social network for videos. The ability to browse videos, share them, comment on them. And Google Video over time will evolve to be much more about metasearch over videos. And these are the two focuses at the current moment."

Mobile traffic is up, up, up, in the Northern Hemisphere, because of the Summer!

"Web search traffic is down from mid-May to mid-July, depending on the weather, from 20 to 40%. The nicer the Summers are, the deeper the slump as less people search on their computer. And usually "mobile" (search, Gmail, map) has either stayed steady or seen the same kind of depth. This is year is amazing: the first 3 weeks in June, "mobile" grew about 10% every week. And then there was the iPhone launch and mobile map was up 40% overnight. "

Why this uptake in Mobile traffic?

"One, people are getting savvy with their mobile device. Two, there is better devices out there. Now the phones are good enough that people can do a search, check their email or get a map."

And what's the fuss about "eye tracking"?

"Eye tracking is super useful. You can basically build an eye track model out of a click model because you can assume there's an even probability that someone that looks for something, they will click on it. And over billion of searches aggregated over time, our click model basically follows the same flow than an eye track. But when you are looking at a new design, it's super useful. As we have that huge dataset to understand what is the click distribution on a page, which then maps the eye distribution on a page."