In my experience (IANAL etc.): If you're being hired solely for your expertise &/or experience, there should not be a non-compete clause in your contract. If you are expecting to some extent to be trained in an emerging field then a non-compete clause may be justified.
Juristiction plays it's part too - I've 'agreed' to such a clause in the past knowing that it was unenforcable as restraint-of-trade under EU legislation.
