Indeed, I was not trying to evangelize SaaS/PaaS :) I'm quite bored of seeing clients wasting founding money on heroku stack, where they first pay incredible amount to have unix processes, then pay a service to have email sending, then one to host uploads, then one to have logging, then on to monitor their app, then they rent a dedicated server anyway because they have specific needs ...

My point is more that it's probably a good thing to provide both webservice and installable app (github, with its github enterprise is a very good example of that, even if way too expansive), to let user choose your product based on what it does instead of what are its requirements and implications.