AdSense has introduced some new ad-unit sizes.
The mobile banner is 320px wide by 50px high, and designed for mobile applications. However if you get your ad-code from AdSense (rather than using Blogger's AdSense gadget), it's available to put onto any type of site. I've put an example of it, and a regular 468x60 banner to show the comparison, at the bottom of the page on this site.
There are also some new widths for link-units: these are available from Blogger's add-a-gadget wizard too - but as always, if you use this you have only limited formatting control, ie cannot use AdSense color palates and cannot centre the text.
I think that Google are doing some experiments with mobile-ad units (ones with big buttons, and a slightly different look) at the moment: I saw some when I used a smartphone to look at a non-mobile-enabled site the other day. Since then, I've enabled the site for mobile access ('cos I discovered that a quarter of the visitors were using mobile devices) - but now when I look at it, the ads inside posts are not mobile, and there are none at the top of bottom (where they were before). So - no conclusions about what we should be doing at the moment, but I suspect that the best-practise here might be changing.
