The overcrowding on the page when it's full is sort of combatted by the pixel list, which shows a list of buyers (ranked by the amount of pixels they purchased, increasing the rewards for spending up big by landing you towards the top of the list).
On top of that, there's also the fact that if you hover over an image you get a tooltip providing a brief note which goes a long way towards clarifying what the site is about. That said, I don't think the actual pixels are where the value lies for those who invest.
It's a novel marketing concept and relatively inexpensive considering the viewers that it's attracted and is likely to continue attracting (Regarding the pixel list). While I was there I clicked a few of the ads that caught my eye, but obviously I don't think that's where the value of the exercise really lies for people who do buy. On that note, I'd be interested to see a hit counter for the various sections of the site, including both the homepage itself and the pixel list section.
Besides, say a company decided to really lash out and purchased a massive block of the advertising space available which eclipsed all the other small ads. I can easily see loads of people clicking it to see what it's about just because it's so much bigger.
Quite aside from all that though, how is this any different to other online marketing? Most of us either block ads completely or have grown accustomed to ignoring them completely, due to the same sort of crowding just spread over a larger scale. Anyone with even a mild interest in marketing will be aware of the difficulties in making people even stop to notice your ads, and what you're looking at on that page is a novel way of presenting ads, and obviously one which is generating at least some interest. Think about it this way, people going to that site are doing so with viewing your ads as a primary purpose, as opposed to having your ads displayed randomly across the Internet and largely ignored because they're on sites where people don't give a shit, or aren't looking to view ads. With the smallest units costing $100, the chance of exposure and having a place in something as unique (Being the Original one of these, I'm aware of the clones but this one is novel in that it was the first) probably makes it fairly worthwhile on its own, regardless of whether it draws mass crowds or not.
Er yeah, I think that's about all from me for now.