Well it depends. Some ministers are little more than figure heads: they know sh!t all about their portfolio, and aren't really that interested in it. They are there to be a parrot, basically. Decisions are made at the centre, and implemented below the minister by the bureaucrats (department heads, etc).
Some are far more hands on. This tends to be true of the important social and economic policy areas -- budget/treasury, health, education, the usual suspects. Those in important portfolios are not there due to any particular interest or knowledge of the area, but because they are powerbrokers (or alternatively, back by powerbrokers). For those two reasons -- important portfolio and backed by powerful factions -- they have to be listened too.
However, it all flies out the window on the approach to an election. Expect a lot of "housekeeping" in the next few months as the government announces are range of "tough on X, Y, Z" policies designed to appeal to marginal voters.
LW.