Although you have said that no replies are necessary, I will reply nevertheless, not least because I use dataforms on a daily basis and am building complete sites around them as well as using them for smaller applications. There are still many wishes that we have lodged with the developers to improve dataforms, but the functionality is up and running and has been working for about a year. And it is very good. I think that dataforms, particularly when combined with ListPages, is an incredibly powerful feature that most other wiki platforms can't come close to matching.
Just for the record, I am currently drafting a new version of the documentation which I hope to release over the next 10 days. This will have images, examples and more information than the current version and might help with some of your questions.
If you want to see a simple dataform where you can see the code used and try it out, there is an example one I created last week in response to a question on the Community site. The lnks are at the end of this post. The permissions are relaxed so you can can create and edit new pages in the relevant category with no problem.
Firstly, when you use a dataform you are basically using a webform and just like the information on any other page the data is stored on Wikidot's servers when the save button on the form is pressed. One dataform page is equivalent to a record in a database table. But it's not a separate database that is embedded: you cannot query the backend directly outside of yur site. You view the data on the page and set up listpages and other features on your site to search and list the data that is stored in the dataform.
A dataform is a way of allowing you to control to an extent the information that your users can enter. It makes it easy for users because they don't need to have any knowledge of wiki syntax at all. And it is often more user-friendly than a standard wiki page because you can upload photos, add links to videos, select from dropdown boxes and radio buttons all at the same time as entering the data. That is one of the main reasons I am building sites with dataforms: it makes life easy for the user.
A dataform page is just a page in a category on your site but it has a special structure and doesn't use the normal wikidot editor. If you need to change data on a form, when you click the edit button the form opens istead of the usual wikidot editor.
Similar to a database, a dataform is made up of fields and labels in a particular structure. The dataform can have text, select, url and wiki fields (and others but those are probably the most common).
A category - let's say it's called "Birds" - can have only one dataform structure. Then you can have as many pages in that category as you want and each one will use the dataform. I usually autonumber dataform pages so you would end up with birds:1, birds:2 etc etc so that all pagenames are unique (the quivalent of a primary key).
You mentioned permissions: these are set in exactly the same way as for pages in any other category in the site manager -> permissions.
Have a look at http://vineyard.wikidot.com/menu:_template so you can see how a dataform is structured. And the current documentation at http://www.wikidot.com/doc:data-forms will also help here. The bottom part of that page, where the [[form]]..[[/form]] tags are is the structure of the dataform. Then the section above the ==== is how you want the dataform layout to look on the page.
Then go to the main page at http://vineyard.wikidot.com/orders:main and click the button under the photo to create a new "record" and try out the dataform. It's not the most exciting example and it uses only select fields, but it will hopefully give you an idea about using it.
An image of a live dataform in use on a working site is below with the result here. On that dataform I have used more types of fields.
The code used on the live template page is below (I've reproduced it because I have locked down the permissions and you wouldn't be able to see the code on the live template page or try out the form). Quite a lot of it isn't relevant to others as it relates to the design of my site, but it will again show the dataform structure at the bottom and the layout of the page above it and it shows how the individual fields are displayed:
The dataform it produces is shown below and when saved gives you the page at http://www.strathpeffervillage.org.uk/event:20111203-dougie-mac
If you have a specific questions about implementing dataforms, do come back to us over at the community forum which is a lot more active than the projects site and where we do the majority of the support.