Giving it up for Lent

I've been noticing over the last few days that many people on Face Book are going to try giving up social networking for Lent.  I'm guessing the reasoning behind such decisions have to do with the amount of time people spend on those sites; time that could otherwise be spent doing something else more constructive.  An admirable quest to be sure- I'm all for living more of life than watching life play out on a screen. (well, except maybe for movies but you know me...)
But I'm wondering, if in giving something time consuming up for Lent will enable us to have time for other things, what will folks planning on filling that "extra" time with?  Anything that we "give up" will be replaced by something.  So unless we think through what we will do in the time we have freed up, we may find ourselves in a bit of a quandary come Ash Wednesday.
And this has less to do with FB than it does the whole concept of giving something up for Lent in the first place. 
When we decide, hopefully with some forethought, assessment of lifestyle and hopefully prayer, to alter our lives for seven weeks, what is the reasoning for doing so?
No answers, just food for thought...