It tastes kind of like yeasty soy sauce that has been boiled down to a salty, thick black spread (or very dark, mushroomy miso). It's great scratched on buttery toast or grilled cheese, or as part of a soup stock. It's made from beer yeast dregs, and is loaded with umami and B vitamins. I highly recommend adding some to soup stock, especially vegetarian soups. It adds a lot of depth. I haven't ever tried marmite (as elblanco mentions), but everything I've read has made them sound similar.
(I'm not Australian. I'm from Michigan, actually...)
The biggest tins (yes, tins) I found of Vegemite was in Colac at local grocery store weighing in at 5Kg. I wish I had a photo. Sounds like you, @silentbicycle have an acquired taste for the stuff. Love offering it to American folk who usually accuse me of trying to poison them. Marmite is similar but there is a distinct taste difference. Both do well as stocks.
They all taste different, but most likely uniformly awful unless you grew up with it.
But can vegetarians eat bacteria? They are animals too.
I'm suggesting it specifically because vegetarian soups tend to have less umami (the savory, "meaty"/MSG flavor). Non-veg cooks can just simmer bones, etc., but vegetarians need to get umami from mushrooms, grilled root vegetables, boiled parmesan reggiano rinds (which are totally awesome, BTW), miso, etc., and vegemite is another option.
It's quite cheap (if you buy it in "I'm going backpacking forever and may not make it back to Australia"-sized jars) and keeps forever (what's it going to do...become more salty?), so it's pretty convenient.
The only group I've seen seriously struggle with the whole "OMG I'm killing bacteria by breathing, what should I do" issue are the Jains, and I find them pretty silly. (I'm not a vegetarian, but when I was...I still found them pretty silly.)
Some vegetarians are amazing cooks, too. Constraints can really drive creativity.
It was all rather eye-rolling. I can definitely see Jains getting in on that nonsense.
I've found it useful time and time again to be wary of recent converts of all stripes, whether it's Veganism, Objectivism, Haskell, etc.
If I remember, enlightenment was not found in the extremes under Kaundinya.
That message really seems to be lost I think. Both in the purposeful following of an extreme ideal, or in not being mindful of extreme habits.
Even if one is not a Buddhist, the concept of the middle path can be wonderfully freeing from expectations of extreme ideologies that sometimes ferment under civilizations.
The popular American impression of Buddhism is pretty weird - historically, it's heavily skewed towards Japanese Zen Buddhism, but secondhand, from the Beats* . The way people talk about Zen, you'd think it had antioxidants or something.
* Due to their infatuation with the San Francisco Zen Center, Shunryu Suzuki, etc.
I guess the best way to compare the two is Guinness extra stout vs. regular Guinness.
Unless you really like it, you probably won't use much of either -- it can go for a very long time. I personally like to use it like a seasoning to add savoriness to my cooking.
It tastes like a combination of steak, Guinness and soy sauce.
That's amazingly accurate except its like a thousand steaks, 1000 pints of Guinness and 1000 litres of soy sauce in a 200ml jar.
It's impossible to get over how intense the taste is. Even a wafer thin coating of it is too much on toast.
The bit that caught my eye, "Australians get a dark-brown spreadable yeast-paste treat called Vegemite, for example". I have a picture of the item being described here ~ http://www.flickr.com/photos/bootload/4961948487/ which came from a PR1M (Patrol Ration One Man) which I used earlier this year marching 240km for a lost bet on house prices ~ http://www.flickr.com/photos/bootload/collections/7215762379...