I would definitely say it Don (like the first part of donald) -uh-vin or vun, depending on how Yorkshire my voice is at that particular moment. But I can definitely hear it in my head the way daegar writes it.

Stress on the first syllable too.

Mind you, my name (Nicola) was pronounced in a real variety of ways when I lived in the US, so I wouldn't be suprised if Donovan had many accented pronunciations. (For my version of Nicola the stress is on the first syllable, so I am NOT a new form of soda drink)