The vast majority of our clients come from referalls/word of mouth, and we usually point them in the direction of the website if they want more info on everything we offer, however we are seeing around 8 to 10 new clients each week coming as a direct result of our website/search engines.
Yes, the downside is, it costs us to market the website, we use google adwords, but it is proving to be cost effective.
I think if you have a large enough client base already, then the cost of marketing and running a website not be worth it.