There's a truism I often hear - claiming that the less complicated the signup process for a web-service, the higher the conversion rate (as a rough measure of complexity, count mouse clicks to signup completion).
Has anyone A/B tested or otherwise measured this impact and reported on their results, comparing a signup process with a "where did you hear about us?" form to one without?
It's different for every product/service, so I'd suggest testing for your own site.
For a relevant but not completely related example, we tested 2 versions of a homepage: a call to action that drove our users directly (1) to our trial sign up form or (2) to a plans and pricing page. While (1) drove over 2x the number of trial conversions, both (1) and (2) resulted in the same number of paid conversions. Had we just looked at "industry standards" we may have come to a different conclusion. Testing your own site is critical.
One suggestion if you are concerned about the potential lower conversion rate - add the "where did you hear about us" field immediately after sign up rather than during sign up. You'll capture a fair number of users that way without impacting signup.
Our company handles this a bit differently. We don't ask the "How did you hear about us" question on the sign-up form. Instead, we wait a few days after the person has gotten into the demo, then we send an email from a salesperson saying something like "Hi, my name is Jack. I'm the customer support rep assigned to your account. Feel free to write or call me if you have any questions. BTW, how did you hear about us?"
It's amazing how many people don't want to talk to anyone they perceive as a salesperson. But they are more than happy to provide us with a simple bit of marketing data. And then since they are writing the email anyway they ask for a price quote, or tell us what they don't like, or whatever.
The bottom line is that this gets the relationship going. Once the relationship has begun, the sale is nearly won. YEE HAW!!!