In the strictest form of their use, quotation marks are used to denote when a character or subject of a story is speaking.
Example: Shmitty lurched his arthritic body down the stairs as he called out, "Morning Sal, you old bastard."
More colloquially, the quotation marks are used to convey irony.
Example: I was speaking with Susan this morning and she said she wouldn't be coming in because she was feeling "sick"; I'm sure it had nothing to do with the fact Barney's is having a sale.
An italicized font however, is meant to do one of two things: it can denote a title of a piece of work such as a book or a periodical or (notice the usage) it can convey emphasis - as in "can you believe that she thinks thinks that's an acceptable choice?" (implying that of all people 'she' should know better).
Anyway people, just a little lesson. Keep it straight out there. In a world where we express ourselves in 160 characters or less 25 times a day, it's never been more important to practice safe grammar and keep your words healthy and meaningful.
