I too am having a custom frame built just-now and, while I have always used threaded in the past, I am having this one built threadless for a few reasons:

- much larger choice of stems
- much larger choice of headsets
- I find the threadless design to be much more efficient and logical, ie the stem clamps straight onto the fork, no fu#king around with headset wrenches and expanding bolts
- I also happen to like the modern aesthetic they have