However, what many may not be considering is the influence the website can have on the top method, "agent referred by others." If you're thinking that continually building your referrals will always be effective, you might want to consider the study done at the Keller Center at Baylor University's Hankamer School of Business, and reported in part by Realtor.org.
From the article:
"They tend to seek out "word-of-mouth" referrals from friends who either are real estate professionals themselves or who have had a positive experience with a particular associate.
They then log online to check out the practitioner's Web site, taking into consideration availability and target neighborhoods."
So, you work to encourage referrals from your previous clients and others, and you're getting some. But, the buyer who's out asking is probably asking several people. This prospect may get two or more referral recommendations. They now appear to be checking out these agents/brokers on the Web, looking at their Internet marketing, and possibly their visibility in social and business networks.
For those still considering a website "a necessary evil" (I just saw this quote in a real estate technology forum.), it should be a concern that you're very possibly getting referred and never hearing about it. If your Web presence isn't up to par, they're going to someone else.

It still amazes me that, in 2009, some would still consider a web presence a “necessary evil”. Unless your business comes 100% from referrals, and you’re getting a TON of them, you’re doing yourself and your clients a disservice by not providing them a web site where they can go to find real estate info they need. NAR reports that about 87% of home buyers start their search on the Internet. To be competitive and relevant in this market, you absolutely need to be there.