That was one funny thread, Spaw, I re-read the first few posts and found myself laughing out loud again.
I don't think I do sing in the shower. I might sort of rehearse whatever song I am in the process of learning, but I do that in the car as well, in fact I sing in the car more than in the shower.
Back in Britain however, when I used to take a bath (which I believe is called a "hot tub" here) it was a different story. You can relax in a bath (or tub) and really let rip. I remember I used to sing "Caledonia" in the bath fairky frequently.
I always thought it would have been a nice touch if Hitchcock had gotten Janet Leigh to sing in the shower just before her untimely demise in "Psycho". Something from Rodgers and Hammerstein, perhaps, "I Feel Pretty" or "I Enjoy Being a Girl".