I have a client that in a previous life bought and spammed a list of 1 million email addresses for a dating site (from a shared hosting account!). They ended up with a couple of thousand users very quickly which is what you need with a dating site. However the spamming incident caused all kinds of pr and blacklist problems which contributed (but not directly caused) the eventual wrapping up of the business.
So it seems to be pretty effective but with downsides depending on your business.