Youngest Daughter is going to Australia and New Zealand in July as a Student Ambassador and in our pre-travel research, we all tried Marmite. We couldn't find Vegemite in our area which is the Australian version of this yeasty spread, so British Marmite was snagged for our table.
It certainly epitomizes the phrase "an acquired taste". It is a salty and slightly bitter paste made of yeast and vegetable extracts. It is suitable for vegans, though Oldest Vegan Daughter would have none of it after the first bite. It does have an interesting social history. Look up marmite on wikipedia and there are numerous pop culture references to the spread and more than one would ever need to know about its manufacture. You can also see a snarky reference to Marmite quoted from Bill Bryson's "Notes from a Small Island", in which he states
There are certain things that you have to be British, or at least older than me, or possibly both, to appreciate: skiffle music, salt-cellars with a single hole, [and] Marmite (an edible yeast extract with the visual properties of an industrial lubricant).
We tried it on toast spread butter first, and then spread with the sticky brown paste. It was OK, but nobody has been quick to reach for the jar since. I did use some Marmite diluted in hot water as a vegetable broth substitute when I was cooking up a casserole and it worked just fine, so we'll keep this cute little brown jar (shaped like the French Marmite cooking pot) in our pantry. But it certainly won't be replacing peanut butter as the stick-to-the-roof-of-your-mouth snack of choice in our household.