One week after I finished my website, I just had my 2 first sign-ups! I focused my whole Monday on promoting and talking about my product in different places (website and forums) so I guess it worked.
However, it doesn't mean that these 2 people will use my product. I have to talk to them and see if they match my criteria (in fact, you can use my product only if you have a certain amount of customers and if you collect data about them).
Plus, my product isn't fully finished so I sent them emails to see if they are interested in becoming early users (I offer them lifetime discounts if they accept).
So now, I just hope they will use my product! Wish me luck :)