I do get a lot of people that talk about Word of Mouth being their number one way to generating new sales. That is great. For many businesses it should be the best source of new leads and it shows you are doing your job well.
So why would you want to build an online lead generation site if your Word of Mouth Marketing is working so well?
First, because you should never count on only one source of new business. You will never hear my say that our lead system should be your only source of business.
Second, because your Word of Mouth cannot be easily controlled. You might get a lot of referrals one month and none the next month.
Third, because Word of Mouth will hit circles of peopel you have had experience with, but will rarely leap the fence and get you into new circles of people. Say that one lead comes from the web and they start talking about you after doing a great job with them – this is probably a big circle of family and friends that have not had experience with you before so the Word of Mouth will be new and more effective in generating more new clients.
Ultimately, you should try many marketing tactics and measure the results and keep building those that have a positive ROI. That includes word of mouth but is not exclusive to word of mouth.