Most adults remember few grammar rules. One that I'm sure will pop up for most is the "never end a sentence with a preposition" rule that they were taught from grade school to high school. This rule causes you to write stuffy, pedantic sentences that no one would ever say out loud.
I have news of great joy for most of you -- it's OK to plop the occasional preposition at the end of a sentence! The Grammar Girl says so; the Phantom Linguist gives us the go-ahead; About.com gives an authoritative "OK."
For the sake of argument and vigilance, some still promote keeping those pesky prepositions from the end of sentences because they are a wimpy way to conclude. Mellanie Spiller seems to be a purist with whom you would need to argue this point. The good folks at Garden of Phrases equivocate a bit. And the Answer people at Yahoo even show you how to rewrite a sentence to make it stronger and more effective while keeping that preposition tucked somewhere in the middle.
In my class, I will allow the occasional preposition to appear at the end. But be advised that I'm gritting my teeth as I deny the teachings of my elders.