I'm not currently using either. I did install a security certificate for email back in May 2005 but did not reinstall it when I installed a new hard drive and reinstalled my OS in Oct 2006 after installing a new hard drive. I do think it's a good idea, yet, I believe, used by very few computer users. I'd guess it's more common in corporate settings than among home or small office users.
I got the certificate from Thawte (thawte.com). Where did you get yours? Have you experienced any problems using it, such as recipients not being able to open mail received from you or being confused by seeing something they were not familiar with?