Hi Graham,
I've never seriously considered it. Folks over on the AGF have posted pictures of some very beautiful and interesting guitars from many different luthiers. However, I've always been uncomfortable with the idea of shelling out a lot of money for a custom. The fact is that I wouldn't even know where to begin. I've only semi-seriously considered having someone build me an 18" super-jumbo 12 string (like the F-612), as one fellow did over in the UMGF forum.
There are some top-end music stores where you can go to sample some of these builders' works. I really haven't done that. Perhaps if I ever do, I might get the bug. Still, more likely is I'd just like one off the shelf and buy it. Commissioning one and waiting a long time for it... well, I'm just not serious enough. Besides, I enjoy collecting Guilds and Ibanez too much to put the money into it.
It may be my perception, but it seems most acoustic guitarists just don't go this route. I mean, you've got JT who started with Olson back in the day (that in itself is an interesting story where Olson just gave him a guitar to play)... But, the vast majority of known players out there seem to buy stock gear. I suspect this is a money thing (starving musician).