I suspect that both individual users and corporations value control over their checkbooks — and ownership of their software — quite a bit and the subscription model will have to be built around substantial incremental value in new software, new access to additional function and support, or other customer seductions to get this idea off the ground.
C. David Gammel, CAE
Helping associations pursue goals that matter.
C. David Gammel, CAE 
Software subscriptions sounds like a fine way to prepay for future services. Regardless of whether this model is adopted or the current, paying for upgrades or “new” products, I see bug-free delivery as a central value. Are we subscribing to updates from bug-free software or still again paying the producer for shoddy work?
Subscriptions probably won’t affect quality of product either way (for example, current version of WinXP will check for updates and patches automatically and download them). What it will do is ensure an income stream for the software vendor which isn’t necessarily in the subscribers best interests or needs.