At the moment I'm using a pre-launch signup page with most traffic driven by adwords. Only time will tell how well it works though, Mint famously managed to get

At the moment I'm using a pre-launch signup page with most traffic driven by adwords. Only time will tell how well it works though, Mint famously managed to get 20,000+ signups this way but most sites will have less of a "wow I need this" factor than Mint. My current conversion rate (i.e. user signing up) is around 25% - I'm not sure if this is good/bad or even reflective of common conversion rates.