Godin makes a fantastic semiacoustic fretless bass with a great sound, a great player.  Not cheap though.

I'd love to have a Martin, but my Larivee 6'er might get jealous (and my bank account/Sr. Management would probably have some objections as well).  I've also been wondering about the feedback issue, but I seem to recall a couple of manufacturers who sold inserts that would dampen the sound hole on an acoustic (which I seem to recall having been done with a coffee lid and masking tape by a few folks as well on the uglier DIY side of things). If I ever needed to play out really loud though, I'd probably consider it.
 
Those Godins also look pretty nice, but as you say, there's still the financial issues to be overcome.  
 
Thanks guys, I certainly appreciate everyone's responses.

I've got a Michael Kelly Dragonfly fretless.  It is what it is, I guess that's the best way to put it.  Some time spent filing the nut and such and it's a pretty decent player.  Not a very acoustically-loud instrument, to be expected with such a small body, and prone to feedback at higher volumes (duh).  It is about perfect for a '40s swing band gig I do occasionally, and nails the upright bass tone as well as anything.  I guy in town recently sold one for $125, so they are out there if you look..  It's a nice tool to have around for those times when an amp is inappropriate or inconvenient..
 
John

I just threw this bit up onto youtube.  It's for a project that never got off the ground, but it should give you an idea of how the Michael Kelly sounds..
 

 
John