In general I prefer the control borders to be only 1px wide but the default in Nintex Forms 2010 is for them all to be 2px wide. Is there a simple way to change this value without formatting each control individually? Ideally this would be a global setting but if I have to do it for each form I can live with it. I just don't want to have to do it for each control.
good question, never thought about that. Afaik there is no global setting or something you can use.
I have one idea though i would like to share. If you open your developer tools while filling out your form, you can inspect the html that's rendered. You will see that almost all of the tags have Nintex classes assigned. In your SharePoint hive, you will find the css files nintex uses for styling (somewhere like C:\Program Files\Common Files\microsoft shared\Web Server Extensions\15\TEMPLATE\LAYOUTS\NintexForms\themes\base). So you COULD create your own CSS file and change the default border width for all Nintex classes. You would then need to reference your own stylesheet in the form settings of each form.
I haven't tried it myself, but sounds like it could work However, this would be quite complex because you have a lot of html and css classes to check.
If you really try this approach, please keep me informed about how it works. This could not only be useful for border-widths, but in general for default layout settings.
You can also start a new feature-request for your issue as this would be very useful for setting global layout defaults.