Having a couple of Ponos with truss rods and a Kanile'a, and previously a Kala without I agree 100% with Ukulelecowboy. The truss rod does give you the opportunity to fine tune neck relief, but it is not a necessity. If it was, then you would see them in most of the high end ukuleles. That said, I like being able to tweak the Ponos a little, but the presence or absence of a truss rod would not be a big part of my trade space in selecting a ukulele.
Larry from Delaware
Kanile'a T-1 Deluxe, Islander MT-4
2000 Collings D1 (Canon), 1993 Larrivee OM-09 cedar top (Lady), Taylor GA-3 12 string, Martin 00C-16DB
Carvin LB-20 fretless bass