I've spent some time building apps on force.com and I have liked the process.
There is a lot of resources out there for you to learn and they seem to be pretty open to how things work.
You'll need to keep in mind governing limits and batch processes as they need to protect the platform but it's a pretty easy to use platform and with over 120,000 clients using the system, if you go ISV you can gain access to all those potential customers.
I've spent some time building apps on force.com and I have liked the process.
There is a lot of resources out there for you to learn and they seem to be pretty open to how things work.
You'll need to keep in mind governing limits and batch processes as they need to protect the platform but it's a pretty easy to use platform and with over 120,000 clients using the system, if you go ISV you can gain access to all those potential customers.
I would check out a local user group to learn more: http://events.developerforce.com/dugs?title=page/Force.com_U...
Also sign up for a free developer account at developer.force.com