Since you can't use italics on Twitter and Facebook, you have to choose some other way to format titles. Here's how Grammar Girl readers voted.
I confess that I've broken my own rule about being consistent. For example, sometimes I put book titles in ALL CAPS, which is the publishing industry internal style and sometimes I put book titles in quotation marks, which is Associated Press style. No matter what I do, I occasionally get complaints from people who think I'm doing it wrong.
I decided to see what everyone else does. Here's the result of a poll I did on the Grammar Girl Facebook page.
People overwhelmingly prefer quotation marks, so that is what I'm going to use from now on.
These were the number of votes:
Quotation Marks: 152
No Formatting: 15
All caps: 14
Flanking underlines: 11
Flanking asterisks: 6
My favorite thing about Google+ is that you can format text.
Related Article: Capitalizing Titles