It depends on the value of the domain. If the name is fairly crappy and unlikely to yield much profit, I do the mass-contacting method with some customization as you say. But valuable domains involve bigger bucks at stake, so those potential buyers get more carefully crafted emails.
In the end, its still best if a company contacts you rather than you contacting them, because you are in a stronger position. But...I know that its hard to wait for companies to contact a person, as its possible they might never get around to doing so.