I think a well-known variation, metered service, will be quite attractive if users are given free monthly 'casual usage' allowances (10 hours a month sounds reasonable).
Software itself will be free to download, but if the usage (measured by the software itself) goes over 'causual usage' allowance for the month, the user will be billed for the extra hours. When the total amount reaches the 'street price' of the software, user gets to own the product outright.
Would I go for this? For software that I want to use brief-but-intensely or for software I intend to use all the time, my answer is yes. But for software that I intend to use to create non-commercial contents with, like Maya ($1999 retail) or 3DS Max ($3500 retail), it is still a lot of money and very poor ROI.
I think we need multiple creative solutions that, together, will bring the magic back into the software business.