The problem that I have with subscription services is that they generally have a one month minimum subscription. As a result, it often feels like a commitment to subscribe to something, and any time spent not using the service, just feels like you are wasting your money. I cant even remember how many times I got a WoW subscription, played it for a week, and then dropped it. If they did daily subscriptions, I would jump right at the chance. Sure, if you were to pay everyday, it would give yourself a huge bill, but just for those days where I fancy playing it, it would be a lot better than a £10 commitment. I would imagine that the same would apply to software. If I had to pay £10 to use Microsoft Word every month, I would probably just find another service to use, because chances are, I would write one thing, and then not touch it again.
That being said, I hate subscriptions, because all they do is inflate the cost of a service. I just wish that things would do away with them. I tend to just prefer the whole "you pay for it, you can use it for as long as you want, as often as you want.".