  We discuss approximability and inapproximability in FPT-time for a large
class of subset problems where a feasible solution $S$ is a subset of the input
data and the value of $S$ is $|S|$. The class handled encompasses many
well-known graph, set, or satisfiability problems such as Dominating Set,
Vertex Cover, Set Cover, Independent Set, Feedback Vertex Set, etc. In a first
time, we introduce the notion of intersective approximability that generalizes
the one of safe approximability and show strong parameterized inapproximability
results for many of the subset problems handled. Then, we study approximability
of these problems with respect to the dual parameter $n-k$ where $n$ is the
size of the instance and $k$ the standard parameter. More precisely, we show
that under such a parameterization, many of these problems, while
W[$\cdot$]-hard, admit parameterized approximation schemata.
