Allow the creation of UDFs which would be local to an install and could be shared easily among users - perhaps in a wiki style forum here as well - a wiki so people can suggest improvements or make the calculation more general or robust.
I would like input on how the UDF could be used between users and workbooks considering they may have parameters in them and will call dimensions and measures with different names. Here's an example of a UDF:
Action: Round a DateTime to the nearest X minutes, where X is passed as part of the UDF call. Maintain the date portion of the DateTime in the rounded time.
Inputs: A DateTime field [DateTime] and an integer with a range of 1 to 30: [Round]