Rob,
I have looked at these as I want one too. I think your better off with a small bowrider though. When I was looking it seemed like alot had new motors and I kept wondering why and I was told the motors in most of these don't last and/or are very costly to repair. It's sucking in alot of salt water, seaweed, and other bay crap. I admit they look fun and have great seating usually.
You got me thinking again, I may start to look as we need something else to do some days where we can tube, wakeboard, waterski, etc. Miss those days when I had a boat that could do all that!
Back to the jet boats, most have the rotax motors which are aluminum crap. A small 18' bowrider you will get a real motor with a I/O. Just as fun. Just as fast. Not as manueverable and will require slightly more water, though can be trimmed up.
Even a outboard is easier. look at the 16' bayliner element.
Just my .02.