Long term I see that as a buying point. Same with CSX, albeit with deeper reservations on CSX's management style. The yield is over 3% and I believe, in general, sustainable (nobody has a payout ratio over about 45%). That said, I intend to look into buying some shares and/or setting buy triggers.
That being said...CP has been chasing NS and if a buyout happens I'm dumping the shares I have ASAP. This is partly because of how *ahem* well mergers tend to go...but more because I strongly disapprove of Hunter Harrison's style.
Disclosure: I directly own shares in NS and CSX, and I believe I'm the beneficiary of some shares of UP as well. To my best knowledge I neither own nor am the beneficiary of any CN, CP, or KCS shares.