I just got my Mac Mini 2 days ago. I am pretty much in the same boat with you but I use Prem. Pro for work. I have wanted to get more familiar with FCP since I get calls to do work on it every now and again.
The verdict? It seems to work. DV editing is functional. I am using an external USB2 drive for media storage currently. Now I am not sure I would use this as a workhorse system, but it does do the job for me so I can get up to speed with FCP. I have yet to do any heavy lifting with it, but simple disolves and titles render out pretty quick. As with most computers, RAM is your friend. I have 512MB right now but will get 1GB as soon as the holidays have passed.
In my case, not a waste of money.
Good luck