Google's new left column gives searchers the opportunity to click on separate sections such as Images, Shopping, Blogs, Updates, etc. Google displays these links, and the order of the links, based on the keyword search. Test for yourself to see how it works.
The problem is that Google identifies its home page as Google Search and these separate sections as Partner Search.
So for AdWords advertisers if you have opted out of Partner Search, you need to opt-in to get your ads listed.
The other problem is that many of these new sections, particularly Shopping, only list 2 ads at the top of the page with no right column. So unless you can afford to be one of the top 2 ads, your ads will not be seen now. No more strategically buying the #3 - #5 spot or working with Position Preference.
The other big problem is that Google essentially dings us for two impressions for just one search. If someone searches "Photoshop" then the SERP shows ads. There is one impression. If the searcher clicks the Shopping link that goes to a new SERP which shows the ad again. There's the second impression.
The problem is that when you do your Analytics you'll see a really low CTR rate for the first SERP and a higher CTR for the second page. It's tempting to think that Google Search is failing while Partner Search is a success. But there's no way to know what is driving the business.
It also unfairly lowers your CTR rate on the first SERP even though Google is the one getting the searcher to leave the first SERP by showing him this new left column. And with lower CTRs comes lower quality scores which results in higher bids.