This is half true
It's unlikely to kill you, but there will be small amounts of current flowing through your body.

Water is actually a relatively poor conductor of electricity, but this is offset by the fact that if the toaster is immersed in it, there is a fuck-load of it to do the conducting. In this case, the resistivity is dominated by what is called spreading resistance: this is a geometry-dependent resistance cause by the fact that close to the electrodes, where the electricity paths all converge, you're relying on a small area to do the conducting, so the resistance is quite high. Far away from the electrode the paths diverge, so the path area is very big and the resistance is therefore much smaller.

Spreading resistance is very geometry dependent, so putting numbers to it is hard, but for a approximately toaster-sized reference, a circular electrode 2cm across in normal tap water will have a minimum spreading resistance of about 500ohms.

Now there are two discharge paths in the bathtub-toaster scenario. One is that the toaster will be shorted by the water, the other goes to earth via the bathtub (assuming that the bathtub is sufficiently conductive). The short-circuit path will encounter the spreading resistance at both electrodes, giving a resistance no smaller than about 1kohm and a current no greater than 0.25A. With a perfectly conductive bathtub, the earth discharge should be no greater than 0.5A. Neither of these currents is sufficient to blow a fuse, but the earth current should trip your RCD.

However, the important thing to remember during your bathtime snack-making escapades it that the current density in such an immersed-electrode scenario is only high close to the electrodes. So if you have a part of your body close to the toaster in the water, you might get that nasty crawling sensation at that part of your body. However, further away from the point electrical contact the current density will be too low to feel. You would probably also have to be trying really hard to actually kill yourself this way.
(Mr T, Wed 6 Oct 2010, 10:12, 3 replies)

Will the toast wet?
Or will the electricity keep it dry? I look forward to your suitably impressive answer.
(The Archduke of South London I'm in your Girlfriend eating her organs, Wed 6 Oct 2010, 10:51, closed)

Ah! That explains a long-standing mystery
I was making tea in a rather drunk state, and I noticed that my hand was tingling. It turns out that when I'd pulled the cord out of the kettle, it had ended up in a pool of water on the worktop. Which I also had my hand in

I always wondered why the sensation was so mild. Now I know.

Yay physics geeks!

Also means that all the films where the hero electrocutes the bad guys are complete pish, though
(moon monkey is busy making memories worth repressing, Wed 6 Oct 2010, 11:01, closed)

Thanks MR T!
I had thought that dropping an electrical appliance into the bath with you would not likely kill you, but was lacking the knowledge of physics and electronics to have any confidence in my theory.
(Me, I'm not... in any way intoxicated, Wed 6 Oct 2010, 19:46, closed)