Some of the main problems surrounding building forms in SharePoint are around look and feel and permissions. Mobile friendly SharePoint forms are often a business requirement and in my opinion should always be a business requirement.
To complicate matters, the native capabilities of SharePoint require the person filling out the form to have write permissions to the SharePoint list. This often conflicts with the business need to keep form data private and restricted to a specific staff segment.
Easily the biggest problem with building SharePoint forms is, well, it’s hard.
Building a custom form is SharePoint requires programming skills, and making mobile friendly SharePoint form requires design skills, and making it function correctly requires time, patience and good fortune.
You owe it to yourself to try this 3rd party SharePoint form builder tool. Full disclosure, it’s made by my company, Kintivo. The Smart Forms Module for SharePoint solves the problems associated with building mobile friendly SharePoint forms. I firmly believe this tool belongs in every SharePoint deployment.
Jim Bob Howard, contributing author to several popular SharePoint books demonstrates the form web part that SHOULD have shipped with SharePoint in this SharePoint form building video.
The resulting mobile friendly SharePoint form posts form submissions to a secure SharePoint list which the submitters may (or may not) have permissions to.
Joel Oleson and I did a webinar a while back about this same SharePoint form building utility entitled Demystifying SharePoint Forms Strategies.
Here’s a white paper about mobile friendly SharePoint forms entitled Forms Are Important.