Thanks everyone who replied.It seems that there's a lot of support for the RDFa route in that (perhaps not statistically significant) sample of opinion. But to summarise my understanding of your various bits of advice: since there aren't currently so many applications out there consuming RDF, a good RDF publisher should provide as many options as possible.
Therefore rather than deciding for either RDFa or a content-negotiated approach, why not do both (and provide a dump file too)
Cheers Bill
