Techcrunch is reporting (http://www.techcrunch.com/2008/08/28/youtube-to-squeeze-more-money-out-of-homepage/) that YouTube will be "leveraging its homepage for profit by selling large format ads that expand to fill the whole page."
In the US it has experimented with click to expand PDAs for Pineapple Express, and this move brings the YouTube homepage in line with other prominent high traffic homepage placements in terms of impactful ad units available to advertisers.
The homepage for YouTube is key as it doesn't include any potential copyright infringements - so it is clear to monetise it as it pleases. It's not so easy with user uploaded videos - unless YouTube has a partner distribution arrangement with them.
The YouTube homepage locally does around 1m impressions a day, which would put it behind ninemsn, the Fairfax mastheads, myspace, News.com.au and Yahoo!7 for sheer volume. One would imagine it would be difficult to charge more than $40k for this placement (given that is the ballpark myspace charge for a full homepage reskin).
Still - one of these per month would generate around half a mil. annually for YouTube - which isn't exactly chump change, but probably doesn't start to scratch the surface on how much the channel wants to make.