Any ideas what's wrong with my code? Another plugin is essentially doing the same thing, but with text/select fields rather than a single checkbox...

I can't get the value to store when you click save, though.

Just use "User Profile fields" vBulletin will then handle all the saving and editing and management of the front-end. It will save you a load of trouble.

You'd typically only be extending the user table if you are releasing a modification, to save modification users the trouble of creating the field. Otherwise it is far easier to stick to User Profile Fields.

(The code you posted looks fine but I haven't messed about much with 3.7.x so I'm not sure how it is changed if at all.)

Yeah, I'll probably end up doing it through the admin cp, but I also want to familiarize myself with vbulletin, so I'd really like to figure out what I did wrong in the code :)

It is always best to start out simple when you are learning.

For example just adding a code manually through the datamanger via. PHP then work onto submitting forms, using hooks, e.t.c. (instead of diving in at the deep end).

I couldn't find a great tutorial or article on what I was trying to do - add a user field manually (instead of via Admin CP). The two datamanager articles I found didn't seem to really apply to me either. Can you help point me in the right direction?

<a href="http://www.vbulletin.com/docs/html/data_managers" target="_blank">Data Managers</a> (Check the "Advanced Datamanager Techniques" section it has something on modification via. Plugins)