A lot of the HL7 stuff could be made a lot simpler if the hospitals embraced a simpler subset--instead, everybody picks and chooses features and fields, as do vendors, and then punt it off to integration work. It's dumb.
IHE has done good work defining conformance profiles on top of the basic HL7 standards that help to improve interoperability. Adoption is growing but still not universal.
For example, IHE WCM (the waveform stuff for realtime signals) is not very good: it is overly textual for the data it represents, doesn't solve all the problems it can run into, has some weirdness with timing and how to map things into HL7, and so forth.
