Main factor which is a barrier to me getting out on the bike as much as I used to is in the shape of a 3 year old son.
That and the fact that I got hooked on mountain biking a couple of years ago and whenever I get spare time I chuck the bike on the roof of the car and go out to put in some miles on my local trails. It's my 'escape' or 'my time' as the wife calls it. The last year has been really busy at work too and I've just finished a year long study course which has involved working at home and weekends to complete set work on time. And whenever I do get the chance to commute I do it on my road (cycle) bike. It kills two birds with one stone , getting out road biking/mtb'ing - it's a fun activity and it keeps me fit.
If I'm honest, although the odd few times I've went out on the Mille just to give it a run, my face has almost split open with me grinning. But I think it may be time to come to a decision on it going. I'll see how I feel after the worst of the winter gets out of the way.