Online ad spend across Europe reached €12.9bn in 2008, representing a 20% growth rate, according to IAB Europe. The pan-regional trade body's annual expenditure report includes data from 19 markets throughout Europe, including, for the first time, data from Croatia, Hungary and Romania.

UK online display ad activity increased by 21% during the first four months of 2009, compared with the same period last year, according to Nielsen Online.

Many advertisers and media planners are slow to experiment with pure numbers online because that’s not what they have done. But that might be changing.