I'm working on creating a JasperReports-based reporting solution for CiviCRM. Because of the way Jasper works, we need to cache report and field definitions that are derived from CiviCRM profiles. This makes it very desireable for us to determine if a profile object has been changed since we last pulled down its definition and compiled it into a Java object. This a appears not to be possible currently, or at least, it seems hard to do.
It would be very useful for this and other reporting software if a "last modified" field was added to the data model for a UF Profile Group, and that the API gave us some way to get at this information.