I don't know if this has been posted before or not, but I just discovered this so I thought I'd point it out. Here is a link to a bass that has a switch on it to convert from fretted to fretless http://www.mikeyguitar.com. A coworker is one of the designer/builders, and said they now have a patent on it. I played one of them just a few minutes ago and couldn't believe how easily and well it worked. There was no gap at all in the fretboard in either mode, i was stunned. My Coworker is also the guy doing the bass playing in the video clips they have on the site. Sorry if this sounds like spam, I am in no way affiliated with the company, other than having a day job working with one of the developers, in a job not at all related to him as an inventor. I just wanted to let everyone know about it, the website doesn't do a good job of telling you what it is they do, but the video clips tell the story great on their own. It really works, and that well, I was left utterly stunned.