Although my primary computer has a perfectly acceptable address book I regularly want this information on one of my other devices (tablet, phone other computer, etc). My case might be a bit extreme in terms of the number of devices I use, but the basic problem applies more widely.

I've used some different synchronisation methods in the past but settled on a web based service I can host on my own website.

I've recently moved my web hosting to a different provider and found the migration surprisingly smooth.

That doesn't mean you can ignore basic data security practices, but it's nice to know things can go well.