Hi Max,
Currently, it is not possible to see what OS or what mail client the recipient uses to open and click on your emails sent using ClickDimensions. However, our web tracking script does gather data on the OS and the browser used by a visitor on your website.
If you include a link within your email to your website that contains the ClickDimensions tracking script, you can correlate the web tracking data and get a better idea of how that person viewed your email.
Don't forget that ClickDimensions emails can also work with Google Analytics if you include a CRM Campaign with your Email Send and make sure the "Add Google Analytics Campaign Tracking" setting (within Advanced Settings of the Email Send record) is set to "yes". This way, you can see if the visitor to your site was brought by a ClickDimensions Email.
More on this here: http://blog.clickdimensions.com/2011/12/google-analytics-email-campaign-integration.html