The cut in tariffs only applies to installations registered on or after 12 December 2011.  It does not apply to installations that are already receiving tariffs.  If you are already receiving tariffs, you will continue to receive your current rate (going up with inflation).

If you register a system on or after 12 December 2011, you will receive the pre-December tariff until 31 March 2012, and then the reduced rate thereafter.

Note that the 12 December 2011 cut-off may be brought forward to 3 March 2012 (if the government loses its appeal against legal action being taken against it).  However, it is safer to assume that the lower tariffs will be applicable from 12 December 2011.