I am always skirting close to the weight limit on checked baggage, in part because I tend to bring lots of books with me when I travel. Even paperbacks can be heavier than you think. Then again, my husband also ends up tossing in a few hardbound books (for work) on any given trip, so that probably doesn't help.
At any rate, even with just clothes and toiletries and normal souvenirs, any suitcase larger than the one just above carry-on size is going to have a very real potential of being overweight. It's also much harder now than it used to be, since 8 years ago most airlines probably had 70 lb weight limits before they started charging. Most dropped it to 50 lbs around 2005 or 2006. When you have 70 lbs to work with, you practically have to pack rocks to be overweight. But when it's only 50 lbs, even seemingly light things add up fast.
I'd much rather play the "reshuffle all the bags" game at home than at the airport, so I always use the bathroom scale method. Sometimes I'll end up with one bag 5 pounds over and the other 10 pounds under, so I try to make sure that I evenly distribute the things that are heavy as well as the things that are bulky but lightweight. The other trick is that most rolling suitcases (which don't have hard sides) protect their contents better if they are full. So it's always a bit of a trick getting them full enough that the lid doesn't cave in without making them heavy enough to be over the weight limit.
On my most recent trip, my husband and I brought two rather enormous checked bags (one was 28" and one was 27", I think), and just barely made it under the 50 lb weight limit. I normally try to travel much lighter than that (we usually will share a checked bag), but this was a three week trip to visit his family, and it will be at least a couple years before we are able to go back. We had a lot of presents to bring with us, and a lot to bring home.
We totally were at least 20 pounds over our limit on the way home, too. We were just lucky that international flights allow 2 checked bags per person, and we traveled there with just one each. We borrowed a duffel bag from my in-laws and put nearly all our books in it. It was the size of a gym bag, and weighed about 16 pounds.