Now that Facebook is asking “What’s on your mind?“, will it leverage its vastly bigger user base and squeeze Twitter out of the market just as the latter was poised to launch into the mainstream?

I believe the question is a valid one. For starters, Facebook’s question is of course a much better one than Twitter’s tired “what are you doing?”, a legacy which defines the service and at the same time has been holding it back. The question as it is being asked now invites countless “having breakfast” and, more recently “watching Rove” tweets and is single-handedly responsible for the high abandon rate of new twitterers.

Only once new users realise that they shouldn’t answer the question “what are you doing”, but rather “what do you find interesting” or, as it were, “what’s on your mind?”, do they begin to find value in their use of Twitter.

Now superficially the signs look good for Facebook’s fending off of Twitter: It has a much broader user base and it is already an integral part of many people’s days.

But there is one crucial difference: Facebook is built around friend connections – people you know in real life. You can stay connected with them and know what’s on their mind. But if you’re anything like me, your Facebook friend list contains many a long-forgotten acquaintance or high school mate whose opinions or preoccupations you don’t really care that much about.

Twitter goes much further than this. Its connections are asymmetrical and non-reciprocal. You do not have to ask people permission to read their Twitter streams. And you can easily follow new people whose thoughts you find interesting and worthwhile.

Facebook may be here to strengthen your real-life relationships, but Twitter is here to extend them.

What do you think? Is the broaden-your-network effect important enough to let Twitter survive? Is it something else that will help it fend off the assault? Or is Twitter doomed to succumb to the Facebook juggernaut?