Not in 2011 for mac. I spent over an hour looking for it recently (based on lots of googling), because had that hour paid off with results, it would have saved me many more.
Do you mean the "View Side by Side" feature? It's not particularly useful: it just arranges two document windows so that they're next to each other and then scrolls them at the same rate. There's no diff computed, so there's no markup of changes, and the documents get out of sync if they have insertions or deletions.
