Peeing in the shower; we've all done it. In fact, some folks even tout it as a way to "go green" saving both water and money. Just pee in the shower, you'll save a flush.
But here's the bummer truth: although you may save water and money by peeing in the shower (or by "letting it mellow" in the toilet overnight") you'll be harming your pipes in the process.
Every time you don't rinse out your shower or flush your toilet, you are laying down a thin layer of calcium deposits. Over time, these layers will build upon themselves until your pipes can end up constricted, requiring snaking or acid treatment with some nasty chemicals to dissolve the sediment. One case we came across was so advanced, it necessitated a replacement of the entire toilet.
Being water wise is important but there are many other ways to achieve this goal. Installing low flow toilets and shower heads, using rain barrels, limiting showers to 5 minutes, these are all great ways to lessen water use. Saving a flush isn't worth the eventual cost to your pipes or your bank account.
So remember, when it comes to #1 -> send it on through, just like #2.