Sessions on a turbo trainer can add to a training regime, they are a good way of doing hard intervals and russian steps etc. But I don't thing they would be of any great benefit as the bulk of training, and would get very boring very quickly. much better to find the time to get out on the bike.

I have to agree that using a turbo trainer will take the fun out of cycling pretty quickly unless it is a part of a structured training program. I'm not saying don't do it but be warned that an hour on the trainer feels like 4 hours on the road. Why not invest in a set of lights and get out there when the family are sleeping. It's what I do when I have not so much time or re-arrange your life so that you can get some training in...i.e. getting up earlier and riding. The thought of doing it is always worse than the reality. If you are adamant about a static trainer and it's purely for weight loss/basic fitness what about a set of rollers? As they tend to keep your mind busier as you need a certain amount of riding technique to stay on the things.