A survey of Good Technology's 4,000 corporate customers found that 36% of the iPads managed by its software were in financial services firms, followed by 11% in tech firms, and 10% in healthcare.
http://www.prnewswire.com/news-releases/heaviest-adoption-of-ipad-in-the-enterprise-coming-from-financial-services-technology-and-healthcare-industries-108151369.html
Here's a pie chart: http://photos.prnewswire.com/prn/20101115/SF01124