I, too, have two...
I work with confidential patient data constantly in my job as a statistical analyst in healthcare research, so my work systems are very tightly controlled. I cannot synch outside devices or programs with my work Lotus Notes GTD system, nor can I keep work email, documents or data in "the cloud". Since my only access to my work system outside of the office is through a laptop VPN connection, it is not practical to have my home system and my work system together.
At home, I have my GTD system running on Lotus notes for work, and I use Toodledo+ Google calendar for my home GTD system with access from laptop, Android Phone, and Nexus 7.
If I need to get input from one system to another (reminders of a phone call I need make during business hours, for example), I just email a reminder to the other system. In addition, as part of my weekly review, I "manually synch" my Lotus Notes and Google calendars by adding work appointments to my "At Work" Google calendar. That way, I have my upcoming work calendar on my phone during meetings. It would be nicer to be able to synch the calendar automatically, but it only takes a few minutes each week.