4D 2004 has a great interface. I like the way their report writer is setup, and overall its a nice application. One weird thing which I definitely don't like is, that after you define a field on a table you cannot remove it. I'm sorry but that doesn't cut it.
The company that produces 4d sells its application for dramatically less then street, much cheaper then FMP. Even though that's a great point in 4d's favor, its not the point driving my decision.
Both FMP and 4d have things that I really like in how they work and things that I don't like.
You also mentioned something that has been nagging me in the background and that's 4d's long term viability. Filemaker is pretty well established and I'm pretty sure it will be there for the long haul (though anyhting can happen). I have no idea about their forums.
I'm very pleased to see such a quick response to my questions here
Thanks
Mike