Monitor support is the issue for me..
My 30" 2560x1600 monitor only supports dual link DVI-D whilst NUC's only have HDMI and DisplayPort. And all the active DisplayPort to dual DVI-D converters on the market are costly (over £60) and have mediocre reviews.
I love the space saving nature of the NUC and am happy to pay extra for it, but I don't want to have to change monitors as well.
The competition is not much better in this regard. Asus Brix also does not offer dual DVI-D, whilst Zotac only appears to offer it on it's older/slower/lower-spec boxes. And Zotac's prices seem to be even more eye-watering than those of the NUC.
Decisions, decisions....