Well, I hope y'all like it. In particular skip down to the bit about information scarcity -- I think that one is broadly applicable to most of the businesses here. (Capsule summary: You can use something which you can create in abundance but which your users/customers perceive as scarce/valuable and trade it to them in return for things which have business value for you.)
Some suggestions i've gotten is to say users can generate 15 widgets per month, but can get unlimited if...they follow us on twitter, facebook friend us, email us to a friend...etc. At the end of the day has anyone seen a case where limiting a free and unlimited product actually increase the number of users?
Particular for businesses that sell products to other businesses, here's what we've found about doing surveys:
* It's easy to drive people to surveys using Twitter.
* They're a fast way to build an opt-in list of people to contact in the future.
* Just asking questions about the problems you address raises awareness and generates leads; for us, more effectively than advertising.
* Most of your assumptions are broken.
* If you're smart, you can build surveys that will generate newsworthy results; survey stories are layups for trade reporters.
We've had a lot of luck incentivizing survey respondants with posters and refrigerator magnets. We're happy to spread those around anyways. Now that we have a solid base of respondants, we're going to look to drive responses with less tangible payoffs. For instance, we'll extrapolate assertions about our industry off survey responses, publish them, embed them in the survey, and wait for nerds like us to come "correct" us.
I'd be perfectly fine with telling users "This survey will be linked to your account.", except that it sounds weird/unnecessary.
Paying customers don't generally expect/desire anonymity. Most probably want you to know their opinion.
A survey like this is little more than a predefined conversation between you and your customers. You're not anonymous in your regular communication (email/phone), so why would you be for the survey?