I thought some people might be interested in comments by George Duke in an interview by Michael Berkeley on BBC's "Private Passions". MB asked Duke if he had a naturally good sense of time. Duke said, basically, no, when he started out he was a "rusher" and had to practice "many, many hours" with a metronome before he developed an even sense of time. He then used that a basis for the less even sense of time he needed to swing, something that he said could be instinctive but could also be learnt.
Anyone who wants to check out the interview can access the programme from the Radio 3 section of the BBC website, at least for the next week or so.
http://www.bbc.co.uk/radio/
The relevant comments about the metronome etc are around 12 minutes into the broadcast. But the whole inteview is worth hearing as an insight into Duke's musical taste and backgrounds (with excerpts from Sly and the Family Stone, Debussy, Haydn, Milton Nascimento and others).