  We discuss some aspects of the deformed W-algebras W_{q,t}[g]. In particular,
we derive an explicit formula for the Kac determinant, and discuss the center
when t^2 is a primitive k-th root of unity. The relation of the structure of
W_{q,t}[g] to the representation ring of the quantum affine algebra U_q(\hat
g), as discovered recently by Frenkel and Reshetikhin, is further elucidated in
some examples.
