I'm about to release a mobile version of my site, and I'm trying to figure out the ad units. Definitely going to use the 320x50 "mobile banner". I'm not totally sure about placement. Are best practices emerging yet? I notice some sites place the banner at the extreme top, above logo, navigation, everything. I'd like to place it closer to the content, but avoid locations near links (accidental click problem). Avoiding the bottom of the "above the fold" space is probably important, since that's where people initiate the finger-scroll action. My idea for placement was below nav, logo and page title, directly above the start of content. Thoughts on that are welcome! I was also thinking about using the 250x250 or 300x250 on some pages (below the fold), but netmeg is making me a little nervous!
The 320x50 banner is *everywhere* in apps and mobile sites, so Google must be aware of what "normal" accidental clicks look like for that size, at least.