"Methinks I'll pass on this one. The common is paying 4.8% so unless rates really take off this issue could become a perpetual discount. "
Don't really think that is a fair comparison. One is taking alot more risk buying the common shares in that the common could fall in value far more quickly and common dividends would need to get cut before prefs, so the prefs payout is safer. Not saying I expect CIBC (or any of the banks) to cut dividends - they have become far too clever at extracting more and more $$ out of folks.....
People buy the prefs for a less volatile investment. 4.4% ain;t bad if you look at the 5yr GOC trading with about a 1% YTM.