You'll love it! May is a good time to go - before the midges swarm in their millions. Put me in mind of going back myself - my family was chucked off Mull in the clearances a few years ago, so I have a soft spot for it. Seriously beautiful and Iona has such a good feel- this tiny hunk of land against the Atlantic (do climb to the top of the central hills). John Smith is buried there. :)