I just read an article on that very topic. The actual research shows that the amount of time it takes to begin doing something consistently and without thought depends, not surprisingly, on the complexity and difficulty of the activity. The easiest habits, like drinking a glass of water after lunch, formed after about three weeks. The most difficult goals could take 8-9 months to become habitual.
I'd place blogging somewhere in between. As each day passes, more people will fall off the wagon. Fewer blogs will be written. Not many people will make it the 100 days or so to make blogging a habit. As for me, I'll quit while I'm ahead and not bother to make a resolution I won't keep.
How about you? Have you resolved to write more this year? Have you seen any statistics affirming or contradicting my assumptions? Regardless, whatever your goals may be, I wish you the best of luck for 2014.