Roger Long wrote:
We all grew up hearing about the danger of oily rags. It was linseed
oil they were talking about, not motor oil. Now that I (hopefully)
will be rubbing oil on teak for the rest of my natural life, I expect
to producing a lot of these little incendiary bombs.

How much of a danger are these left over rags?
...

I found this link, which include (about a third of the way down) a
good discussion of the issue.

http://www.woodworkersjournal.com/ez.../webreview.cfm

The oils that are dangerous are "drying oils," in particular nut oils
such as Linseed, Walnut, and Tung, while non-drying, such as canola,
corn, peanut, motor oil, etc. do not spontaneously combust.

One claim was that pure tung oil oxidizes so slowly that it is not a
danger, but that some "tung oil finishes" are mostly linseed, and thus
are extremely dangerous.

Personally, I've avoided even having linseed on the boat, having seen
the results of spontaneous combustion a few times. My previous boat
had a lot of gorgeous teak in the cockpit (seats, grate, etc) and I
went through the various stages of oiling and various finishes.
Finally, I settled on washing once a season with Washing Soda, which
restores the natural look for a few weeks, and otherwise letting it
turn grey.

My current boat has not an inch of wood on the exterior.