Martin Fowler is another noted professional raising various critiques of the OMG's Model Driven Architecture. One interesting insight of his has been partitioning the UML community by usage: UMLAsSketch, UMLAsBlueprint, and UMLAsProgrammingLanguage.
I would propose a fourth, probably orthogonal concept: UMLAsOoErd (UmlAsOoDdl or UmlAsOql also came to mind.)
As an ex-data professional, I found UML class diagrams to be intuitive and useful, and as I have moved further into the metadata domain with its requirements for deep subtyping hierarchies, recursion, and many to many relationships I've found UML preferable to classic E/R modeling. I also have very much appreciated the open semantics of OMG metamodels; while complex, they are reasonably internally consistent, and unlike ISO/ANSI or IEEE standards, are freely available to anyone who wants to monkey with them. (I still haven't laid my hands on a copy of the IEEE 11179 metadata standard, primarily because of the cost.)
No comparable standards activity to my knowledge is currently based on E/R modeling, and work based on XML Schemas lacks an inherent visual formalism. (Even the UML critics agree that data models are useful, and that's exactly what a class model is!)
The further advantage of UML is that, since the metamodel foundation is rigorous, a well-specified UML class diagram can (via XMI, with the right tooling) be directly translated into an OO persistence architecture. Presto - no object/relational "impedance mismatch"! This continues to be a puzzler for me, why more hasn't been done with MOF/UML as a logical alternative to OQL and SQL 2002.
I am not currently using UML Activity Diagrams much (although I've seen some motion towards using them in the BPM space). I tend to agree that past a certain point using UML to model behavior runs into problems discovered with flowcharts 30 years ago. But I also haven't worked with any true MDA tooling, and wonder how much of the criticism we're hearing levelled is based on real hands-on experience with state of the art MDA tools. I'm at least reserving judgement until I've had such experience.
