Here are the last four regular season games played by recent grand final winners (final position of opponents in brackets).
2010 Dragons: Manly (8th), Canberra (7th), Newcastle (11th), Souths (9th)
2009 Storm*: Newcastle (7th), Manly (5th), Roosters (16th), Warriors (14th)
2008 Manly: Souths (14th), Tigers (10th), Titans (13th), Penrith (12th)
2007 Storm*: Brisbane (8th), Parramatta (5th), Bulldogs (6th), Titans (12th)
2006 Broncos: Storm (1st), Bulldogs (2nd), Parramatta (8th), Warriors (10th)
* yes I know.
I really don't know that you can draw any strong conclusions from this. If anything, these results suggest that you don't want to be playing a good team in the couple of weeks before the finals begin (there hasn't been a winner in five years who played a top five team) but I'd suggest it's more likely that there's no correlation at all. Playing a pair of patsies in the last two games didn't do Melbourne any harm in 2009, though then again an illegal playing roster probably helped too…
+1for this, also what was our run home in 2005?