We use IE8 as a standard browser in the company.
We are using Nintex forms and i read Nintex recommend IE9 but you can use IE8 with limited functionality.
Does anyone have a list of the issues with IE8 and Nintex forms?
Currently, there is not a list of issues of Nintex Forms working on IE8, but you could consider the following.
You will have the same problems and restrictions that you currently have for Sharepoint. For example URL lengths. etc. Take a look at https://technet.microsoft.com/en-us/library/ff919562(v=office.14).aspx
You also must think about issues associated to used libraries as jquery.
You can google "jquery 1.10.1 ie8 issues" or also "ajaxtoolkit ie8"
I don't think that all issues will be present on Nintex Forms, but it's a good start to build your test cases.