No matter how hard digital forms try to convince me that they're anonymous, I never believe them. As a result, I omit the types of suggestions these forms are meant to facilitate - ones that I'd be uncomfortable sharing in person. The only way to guarantee truly anonymous feedback is for there to be no connection between the person submitting feedback and the feedback itself.
One solution to this problem is to setup a typewriter next a suggestion box. This way employees or customers can freely write their impressions without concern about repercussions. Notes written on a typewriter are preferable to handwritten ones because they're less identifiable. And, because typewriter do not keep logs of who used them, there's no need to worry about pseudo-anonymity.
Increasingly, I'm finding situations that benefit more from analog solutions than fully featured digital ones.