Certainly more than I knew about candles. I've seen mentions of "trimming wicks", but this explains why people did it and why we don't need to anymore. The center of a flame has less oxygen and is cooler than the edge. As old-fashioned candles burn down, the wick is in the cool part of the flame, so it would just smoke rather than burning up. Then, some clever person redesigned wicks (how?) so that they bend as they burn. This put the end of the wick in the hot part of the flame, so there's no excess wick make smoke.
When you put a candle out, the smoke is actually wax particles. Put a lit match in the cloud not too far from the wick, and the wax particles will catch fire and the fire will travel down the cloud to the still hot wick and relight the candle.
The idea that such a tremendous amount of labor get saved by improving the wick delights me. I'm sure there's a lot of good stuff of the same kind yet to be invented.
And speaking of cleverness, I just found a nice feature of the strip of auto-tags at the top of some lj commenting formats. In mine, it's a thin blue strip-- if I put my cursor over it, it expands into about a dozen tag buttons. If I highlight the text for the tag, it will automatically be inserted into the text when I click on the tag. The only way I think it could be improved would be for me to be able to substitute blockquote for one the tags I don't use.
Link from the comments at Kate Harding's Shapely Prose
More from the comments: Disapproving Rabbits.