We’re using the custom fields to keep up with a numbers associated with our tasks…these can be numbers ( + and -), currency, percentages, etc. It would be terrific to have the ability to format numbers properly…think of the options you get in an excel spreadsheet cell for instance… This would be useful as you are quickly scanning a lot of tasks. Currently the numbers all look the same, no differentiation. Thanks!
Quick word to let you know we are introducing new types of custom fields in Asana and currency and percentages are among those custom fields. 
You can learn more about it in the following post: Introducing Percentage & Currency Custom Fields + Averages for numeric custom fields!
I hope you enjoy it! Please let us know if you have any follow-up question or feedback!