Reading some of the posts I think people are getting the wrong idea. If two people are flying you can check "two" bags. That's a total of 100 lbs of "stuff" plus two carry on bags that can be up to 80 lbs (on most U.S. airlines) total weight. That's 90 lbs. for one person.
If two people can't do a seven day cruise with 180 lbs. of "stuff" then you really need to rethink your packing.
If you are traveling with children and they have their own seats then they also get one checked, fifty pound, bag but as 2Littletime pointed out, you need the extra hands for the kids and their "stuff".
I really love Freestyle and Country Club casual lines like NCL, Azamara and Oceania. No formal wear or jackets really lightens the load plus onboard laundry helps. We did our last Baltic cruise with one suitcase and two carry on bags.
Another thing to pay attention to is the actual weight of your suitcases. If your suitcase weighs more than 15 lbs. I would seriously consider buying some lightweight luggage.