Collecting identifying information about users filling in a Google Docs forms

Question

How can I get Google Docs to register IDs of people taking a survey generated from by the form?

I have a database of users and I'd like them to take a survey and also have the form link with their ID so I know which of my users completed the form.

Is it also possible to style a Google Docs form or do I have to stick with one of the few styles provided by Google?

Is all of this possible with Google Docs?

_{If not, I may look into SurveyMonkey if it provides these features.}

Answer 1

I only seem to have some bad news for you.

1. It is not possible to customize Google Docs Forms in another way than using the provided themes. (See Google employee AnaLikesLattes' answer)
2. It is not possible to enforce one-submission-per-person but you could maybe use required fields asking for first/last name or email. (Google Docs Help discussion)

I'm not sure about SurveyMonkey (haven't used it) but for more advanced surveys I'd suggest using SurveyGizmo. They offer a free account with 250 responses per month. Comparison of their plan features here.