The back end of my bike, even when new, just seemed too "squirrelly" when I was in broad sweepers at speeds greater than 35 mph. I adjusted air pressure in the shocks and tires, and while I was admittedly a new rider (as an adult on a full-sized road bike), I did ride dirt bikes alot as a kid, many times on roads (illegally) so I knew something about dynamics in turns. The bike just never felt planted all the time, I guess would be the most accurate statement. Plus it bottomed out alot, even at 50 lbs of pressure in the shocks, when I put my wife on the back (not a big girl by any means.)
When I took the MSF course I asked about the sensation I was expereincing, and the lead instructor (who was riding the '11 CVO version of my Ultra Limited) told me it was likely the suspension. He explained to me that it was an older design and that newer suspension kits were available to overcome some of that 'traditional' Harley handling from years gone by.
I don't know if this was gospel, but I did decide to upgrade to the Progressives when I needed new tires, so I combined some new 444s out back with monotube cartridges in the front and a set of Michelin Commander II tires. The bike is now a completely different animal.
The biggest difference I feel is that I no longer have to fight to hold the bike into a lean in broad sweepers; it seems to just easily fall into those curves and feels very stable. The suspension feels firm but not overly-so (I have the heavy duy springs on the 444s instead of the regular ones; I weigh 250 lbs at 6 foot 4) and my wife agrees that the ride is much less jarring even though it feels firmer.
I hope this helps.