This morning I saw a first-hand example of why links to your web site from other sites can be so effective. I was looking at the Google Analytics for the hobby site that I run for the Austin Scale Modeler's Society. The traffic for that site has been pretty steady overall. But I noticed a huge spike in February - five times the normal number of visits.
Digging deeper, I saw that almost all of that traffic was in a 3 day span in February. I thought there was no way this traffic was legitimate, must be some kind of DOS attack, or something. I looked at the geographic stats, fully expecting a spike in overseas traffic in that time period. But it wasn't there. As usual, most of the traffic was from the States. I looked at the content analysis and saw that most of the traffic was to the home page, so not much enlightenment there.
Finally, I started looking at the referral information to see where it was all coming from. Turns out all that traffic was being generated from one site - HyperScale - that had a link to our home page in their "What's New" round-up on Feb 12. I recalled contacting them and asking them for a link on their site. Boy, did it work!
This is not a commercial site, so I don't know how many sales conversions that would have resulted in, but I can't see how a 5-fold increase in visitors could have hurt. Just goes to show that taking the time to "pound the pavement" for reciprocal links can really pay off.