I encrypt work email whenever it includes private or sensitive information. But that is only because my company has a global email address book and every single user has published encryption certificates. My company has also mandated that every email gets digitally signed, whether it is encrypted or not.
Which brings me to my no answer, my personal email. I would encrypt all personal email if I could, but the problem is that it is unlikely I could get all of my email recipients (or even most of them) to bother to deal with keys and making sure their email client could decrypt as required. Not only that, I use webmail a lot and it's not easy to get everyone onboard the same scheme that would allow encrypted email via webmail.
If everyone did it, then heck yes I'd encrypt all of my personal email too. If it was as easy as microsoft putting a big button "enable encryption", along with another button "send public key to email correspondent", then everyone would be using encrypted email. But they won't, so I'm pretty much out of luck.