Darren Rowse at Problogger has the scoop where he has discovered that Google Adsense are testing new ad formats that allow bloggers to have greater control over how many ads are show and what the overall size of the ad block is.

The recent upsurge in activity and development at Google’s Adsense comes at a time where their once dominant market share in contextual advertising is potentially being threatened by the emergence of new competitors, including Yahoo!

(editors note: parallels to Microsoft/IE and Firefox??)