Ponemon Research as made study for Juniper Networks. The study (pdf) reports the numbers and types of security incidents among US based companies. The study is based on interviews with the CTOs, CSOs and CIOs of 583 North American companies of varying sizes.
The study shows that 90 percent had been hacked within the last year, and that 60 percent had been hacked more than once, also within the last 12 month. Of the respondents in the survey around half claims that the security breach happen due to not enough resource allotted to cyber security and the other half claims it is because of the complexity of the networks and technology.
In my opinion the analysis is somewhat narrow, as it has been conducted as an online survey; the smallest respondent has 500 employees, thereby missing an entire sector of small and medium sized businesses. Also I think the study is quite interesting to read and gives a good and accurate view of the situation for the US. It would be nearly impossible to make a similar study in Europe, as there are no requirements of companies to inform of security breaches, thereby making an online survey more vulnerable to inaccuracies because there is no reference data to compare it to.
Postscript: My RSS feed reader just showed that my local CERT just picked up this report also.