I was surprised to not find this already in the idea exchange. Maybe its because I am on my 13th hour today.. so if this is duplicate please accept my apologies.
One thing I have been very frustrated with custom forms is how the data fields are displayed once the form is rendered. In the custom form setup you basically have two options, do I want this field to be next to the one before it or do I want it to be underneath it. If you get too many side by side fields then it rolls over to the next line anyway. Even Microsoft Access lets you design custom forms on a grid.
At least with dashboards you have the option of choosing some basic layouts (see image). Would it be so difficult to give us the same layout options for custom forms?
So I humbly submit this idea - "Custom Form layouts".
If you feel as frustrated with the look and feel of your custom forms I would appreciate your votes!